Category Archives: Western US

LA Fire Weather Forecast for October 30, 2019

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NASA satellite Moderate Resolution Imaging Spectroradiometer (MODIS) image of the Getty Fire on October 28, 2019, shortly after the fire began. Smoke is visible billowing offshore to the south.

“Extremely critical” fire weather conditions are forecast to impact a large part of Southern California, with the strongest Santa Ana wind event of the year possibly occurring Wednesday before some improvement Friday. Affected areas include the entire Los Angeles metro area, where the Getty Fire continues to burn. Wind gusts at or above 70 mph in higher elevations coupled with very dry air (relative humidity less than 10%) will make it incredibly difficult to make any progress towards containing this fire, and presents a high risk for new fires to start.

  • Weather Prediction Center surface forecast for 5AM PDT Wednesday
  • Weather Prediction Center surface forecast for 5PM PDT Thursday

Synoptic Set Up
Believe it or not, the strength of the Santa Ana winds will be tied directly to the very cold air mass moving into the Great Basin. A low along the leading edge of this cold air has caused a massive ongoing snowstorm across much of Colorado. Behind this, cold, stable air will move in along with a strong area of high pressure with surface pressures forecast above 1040 mb. At the same time, a coastal low will sweep south along the northern and central CA coast along the leading edge of the colder air accompanying this high pressure. This will set up a tight pressure gradient at the coast favoring strong offshore east-northeast winds, with local forecast offices citing model output of as much as 10-12 mb gradient from Barstow to LAX, over a distance of only 200 miles.

Impacts
With the tight pressure gradient forecast above, forecasters are calling for the possibility of gusts in excess of 70 mph in the mountain ranges near the coast with, with lower wind gusts of 35-40 mph at lower elevations. The influx of cold air already less capable of holding moisture that will downslope off coastal ranges and towards the ocean will yield relative humidities of 3-8% (as the air dries further during downsloping due to compressional warming). Santa Ana winds of this magnitude along with such dry conditions easily warrant the Storm Prediction Center designation of extremely critical fire weather.

  • GFS model output forecast sounding for KLAX at 11AM PDT Wednesday. Note the huge gap between the green dew point line and red environmental temperature line at the surface (5°F dew point, 64°F temperature). This will result in extremely low relative humidity values.
  • Storm Prediction Center fire weather outlook for Wednesday

Timing
Peak potential for winds appears to be during the overnight hours through morning and early afternoon Wednesday. This is the time when the pressure gradient will be maximized. The high pressure referenced above is forecast to weaken overnight into Thursday, while the coastal low should also dissipate. The high pressure is forecast to continue weakening into the weekend, thus ending the most dangerous period of fire weather.

WxChallenge for Portland International Airport (KPDX) | Sept 25-28

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Temporary Changes to this Blog

Over the next few weeks, I’m going to take a break from my normal posts about weather in NYC and the region because I’m participating in the WxChallenge national weather forecasting competition. This is a course requirement for the final semester of the Undergraduate Certificate in Weather Forecasting program with Penn State University’s World Campus that I’m enrolled in. During the course of this competition, I will be providing forecasts of high temperatures, low temperatures, maximum sustained winds, and total precipitation for various cities in the challenge. The first of these cities will be Portland, Oregon – specifically Portland International Airport (KPDX). If events of particular interest, such as severe weather, tropical storms, or etc are forecast to occur in NYC, I will make special posts regarding such events.

Forecasting for KPDX September 25-28, 2018

Synoptic Set Up (The Big Picture)

High pressure was located at the surface west of KPDX. A rex blocking pattern existed over the Pacific (a upper level high directly north of an upper level low, see animation below, the upper level high is west of OR/WA and shaded with some light blues, the upper level low just south of it shaded with oranges/reds). Some northeasterly winds were forecast during the forecast days, especially later in the day/overnight, which given the topography surrounding KPDX would lead to some downsloping. Still, northwesterly was forecast to be the predominant wind direction, which aligns well with climatological norms for September. A thermal low was mentioned to be in place through the mid-week period that would migrate daily from west to east.

Forecast Rationale

The synoptic set up favors little change in day-to-day conditions. Downsloping and the presence of a thermal low over the Willamette Valley suggest warmer than climatological and MOS (Model Output Statistics) guidance max temps. Despite mostly clear to clear skies throughout the forecast period, radiational cooling at night should be limited due to winds expected to be easterly overnight. When there are clear skies with no/calm winds, this allows infrared radiation to efficiently escape into space from the Earth’s surface, resulting in cooler temperatures when compared with a cloudy and/or windy night. Of note, easterly winds produce the fastest winds for KPDX due to some funneling effects from the Columbia River Gorge (think of this like blowing through a straw). This was referenced in the local forecast AFD. However, the MOS guidance didn’t really show a clear signal of wind directions favorable to strong funneling, so it would be unwise to go too much above guidance here. Late week cool down noted as the rex block breaks down and the upper low that was associated with makes its way towards the west coast. Exact placement/timing could bring some precipitation in the picture by the weekend and maybe early into week 2 forecast period.

Forecast Submitted

Forecast Day Max Temp (°F) Min Temp (°F) Max Sustained Wind

(knots)

 Precipitation (inches)
09/25/2018 82 52 15 0.00
09/26/2018 82 52 11 0.00
09/27/2018 85 54 8 0.00
09/28/2018 83 55 6 0.00

NYC Weekend Weather – Feb 16, 2018

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This holiday weekend will feature some wild swings in temperature. We’ll bookend the weekend with chances for rain, but in between, we may see some decent accumulating snow. So much for an early spring.

Rest of today (Lunar New Year) – the year of the dog arrives on a cloudy day with temperatures dropping through the course of the day on the heels of a couple cold fronts pushing through. We have a break in the rain right now, but more will arrive later in the day. Winds turn to the northwest behind the front and increase in speed, bringing in a much colder air mass that will set the stage for snow on Saturday.

Saturday – much colder with temperatures topping out around 40°F after a very cold start. Increasing clouds as an area of low pressure developing off the Mid-Atlantic coast brings us the chance for accumulating snow. This coastal storm should be fairly fast mover, but forecasters think it will still bring enough precipitation to warrant a winter storm watch. The official forecasts are calling for a range of 4-8″ overnight Saturday into Sunday. Based on current forecast ensembles, I’m inclined to side with the lower end of that range and call for 4″ at best. As usual, the exact timing and track of this storm could still change a bit before the actual event. A slightly slower or slightly more northerly track would result in higher totals, and conversely a faster and more southerly track would result in only minor accumulations.

Sunday – warmer with high temperatures in the mid-40s and decreasing clouds. Whatever snow we get will begin to melt almost immediately.

Monday (President’s Day) – warmer still with high temperatures in the low-50s and chances for rain as a warm front approaches.

 

 

 

 

NYC Weekend Weather & West Coast Storm – Dec 2, 2014

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It’s been a up and down week for weather in NYC, with Monday starting out in the mid-60s, then a colder mid-week that featured some mixed precipitation and rain. The end of this week will feature rain and slightly warmer temperatures by Saturday, then a return to colder conditions Sunday into next week. I’m also going to point out some of the spectacular weather brought on by a huge Pacific storm that hit California this week.

Thursday – the remainder of today will be pleasant and sunny, though cold with high temps only in the low 40s.

Friday – clouds will begin to build overnight tonight ahead of the a storm system moving in from the Southern Plains to the Ohio Valley. There is a small chance for scattered showers, otherwise expecting a cloudy day with highs in the mid-40s.

Saturday – rain should overspread the area by Friday night into Saturday. This storm system will be drawing on energy and moisture from the Pacific storm that slammed California earlier this week (discussed below). Combined with influx of Gulf moisture, this setup favors a moderate to at times heavy rain event for Saturday. Temperatures will rise steadily ahead of this storm system as it pushes warm air up. High temperatures Saturday should reach into the mid-50s despite rain and clouds.

gfs_namer_042_1000_850_thick
GFS model output for overnight Friday into Saturday

Sunday – rain should end overnight Saturday, and high pressure from Canada should quickly build in behind this storm system. The positioning of this high pressure, along with the exiting low, will make for a tight pressure gradient, which should allow for stiff northwest winds perhaps in the 15-25mph range. Temperatures will drop back into the low 40s with the arrival the colder Canadian air.

gfs_namer_084_1000_850_thick
GFS model output for Sunday night

Monday – the storm system from Saturday will move offshore, but it appears from model runs that there’s some chance the storm lingers. As the high pressure from Sunday moves off to the northeast, the clockwise flow behind it may draw this offshore area of low pressure back into the area. This could lead to some rain on Monday. It’ll be a mostly cloudy day otherwise with highs in the low 40s.

Pacific Storm Slams California

Earlier this week, California got slammed by a very strong Pacific low. This storm brought on furious rains that dropped 1″+ in many areas of Northern California, with totals as high as 3-4″ in spots near the Coast Range and Sierra, as well as further south in the mountains east of San Diego. These totals represent more rainfall than had fallen in many of these areas all of last year.

You can see from the map below which overlays drought conditions (the deeper the red, the more extreme the drought, with the darkest red representing extreme/record-breaking drought) with rainfall totals from yesterday. You’ll see that much of the heaviest rain did fall over regions worst affected by drought. Sadly, though this is a case of too much of a good thing, as much of this desperately needed rainfall occurred so quickly, it will simply runoff back into the ocean.

Screen Shot 2014-12-04 at 12.08.35 PM
Map of California with drought condition layer (reds/oranges), and rainfall totals from yesterday

NYC Weather Update – Mar 27, 2014

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We’re entering into a pattern of active weather through the weekend and into early next week. Today will be dry and pleasant, though well below normal with highs only in the mid 40s.

High pressure will move east of NYC before a cold front approaches from our west on Friday. Southwest flow around the high pressure center and ahead of the frontal boundary will usher in milder, moist air from the southeast. Temperatures on Friday will be near normal in the mid 50s. As the front passes through, expect periodic rain showers throughout the afternoon hours.

Saturday – a second frontal system is forecast to spawn a low that will track offshore of the East Coast, bringing a second round of rain to the area. This round will be heavier than Friday’s, with ample moisture available for the storm to draw on. With the clouds and rain, high temperatures will be suppressed to around 50.

Sunday – there is some uncertainty about how quickly the low impacting us Saturday will exit the region. At this time, it does appear that rain will continue through portions of the day. Should the low be slow to exit, colder air could work into the system allowing for accumulating snow Sunday night! High temperatures Sunday will be in the mid 40s.

Monday – should be a fair day, dry, with high temperatures near normal in the mid 50s. So, even if it snows on Sunday, the snow will melt rapidly. Next shot at precipitation comes with another frontal system Tuesday.

Check out the cumulative quantitative precipitation forecast from the National Weather Service’s Weather Prediction Center for Thursday through Sunday morning. Note that our area is forecast to receive as much as 2.5″ of precipitation through Sunday. Also, there are pockets of as much as 4-6″ of precipitation forecast for the West Coast. For California, that’s some good news as it will help with the drought conditions, but as we saw with Oso, Washington mudslide this much precipitation in such a short span of time can lead to landslides. This is especially the case for Oregon and Washington which are no longer as drought-stricken and soil saturated from previous storms.

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Below is a NAVGEM forecast model run depicting two storms simultaneously impacting the West Coast and the Northeast on Sunday.

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NYC Weather – Spring Climate Outlook – Mar 20, 2014

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Today is the vernal equinox and marks the first day of astronomical spring (because as next week will show, even though it is technically ‘spring’, it won’t feel that way from a weather or climatological perspective).

The equinox denotes the precise date when the sun is directly overhead of the equator at noon. Although it is popularly stated that the equinox is also the date when the length of day and night are equal, this is not necessarily true depending on where you are on the planet. For example, the exact length of daylight for NYC today is 12 hours and 8 minutes, according to astronomical data from Weather Underground. That means the actual equinox for NYC occurred a couple of days ago.

Spring Climate Outlook

This is a good time for us to look ahead towards the forecast climate trends for the United States. Below you’ll see a map showing the Climate Prediction Center’s three-month outlook for both temperature and precipitation. Note that the northern tier of the US is forecast to have anywhere between 33% and 40% chances of a cooler than average spring, while much of the southern and western US is forecast to have between 33% and 50% chances of a warmer than average spring. California in particular is forecast to have 50% chance of warmer than average spring, combined with 33%-40% chance of below normal precipitation, which will be conducive for the persistence of the severe drought in the region.

NYC and the surrounding region is in a zone of equal chances, meaning there’s no strong indication as to whether we’ll have an above, below, or normal spring in terms of both temperature and precipitation.

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NYC Weather Update – Mar 17, 2014

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We were fortunate to avoid a white Monday, as our friends to the south in NJ, DC, and Philadelphia got hit with between 4-9″ of snow during this last storm. Once again, despite temperatures being cold enough, we missed the area with higher moisture content, and dry air took the day, leading to some light flurries but no accumulation.

Check out the snow total map for the DC, Maryland, Delaware, and Southern NJ region below:

Screen shot 2014-03-17 at 3.18.53 PM

Looking ahead to the rest of the week, it looks like the formal start of Spring will bring a significant warmup for the area.

Tuesday – A sunny day as the departing storm and associated clouds clear out overnight. Good conditions for radiational cooling will mean a cold start to the day with lows in the mid 20s. However, ample sun will boost high temps up to near 40.

Wednesday – the next storm system approaches overnight Tuesday into Wednesday. A low pressure center will pass over the Great Lakes and to our north, with an accompanying trailing cold front. Temps ahead of the cold front will warm up to near normal for this time of year in the upper 40s, near 50. The cold front will bring along light showery precipitation during the afternoon Wednesday. See forecast diagram from the National Weather Service below:

Screen shot 2014-03-17 at 3.12.38 PM

End of the week will feature high pressure over the area with milder temps near the seasonal average of 50, and fair conditions. The next storm system is forecast to enter the area Friday night into Saturday.

Strong Pacific Storm Possible 10 Days

Parts of the west coast continue to see some abatement of drought conditions, with significant improvement for portions of Oregon and Northern California. Nine of twelve GFS model ensemble members are forecasting a strong Pacific storm coming ashore mid-week next week, which is good news for areas that could definitely use the rain. Below are two of the ensemble members. Note the fairly tight isobars denoting pressure, indicating a strong low pressure center.Screen shot 2014-03-17 at 3.11.55 PM

Really Cool Graphic – All Reports of Severe Hail from 1950-2013

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Another neat graphic from Storm Prediction Center’s SVRGIS: all reports of severe hail over .25″ in diameter from 1950-2013! Again, note the relative scarcity of severe hail west of the Rockies, but look at the density of hail reports over Mississippi and Georgia. Also, check out the dense patch of hail reports just east of the Front Range in Colorado.
hail

NYC Weather Update, Monday Storm – Mar 1, 2014

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Summary

March is coming in like a lion this year (let’s hope it leaves like a lamb), with yet another snow storm to add to our misery here in the NYC area Sunday night into Monday night.

Background

A strong coastal storm that’s currently pummeling California with heavy rain and snow will be transferring its energy and moisture to the aforementioned storm. For California, the rain and snow is a mixed blessing: with a hundred-year drought gripping the region, moisture is welcome; however, so much rain in such a short time window is leading to flash flooding, mudslides, and other headaches. See the video below:

Forecast

Our local NWS forecast office has issued a winter storm watch for Long Island, NYC, and central NJ on south. The latest snow maker will be two waves of low pressure that will travel along the length of an arctic cold front Sunday and Monday. This cold front will across our area during this period, ensuring that the air will be cold enough for all snow during the strongest part of the storm, although precipitation may start off as a rain/snow mix during the day Sunday with highs expected to be in the mid 30s.

The forecast graphic below depicts probabilities of snowfall accumulations at least 6″ or more across the region from 8PM Sunday through 8PM Monday. As you can see, we are right on the cusp of a high confidence zone for more than 6″. As it stands, 6″ seems to be the going number for the areas under the winter storm watch. A slight northward adjustment of the storm track would increase the chances we get more than 8″.

This will be a prolonged weather event – so, moderate snow for a longer time, but less of the heavy snow that we saw with the last storm.

Screen shot 2014-03-01 at 1.50.16 PMOvernight lows on Sunday will be around 20 in the city, and highs Monday will be in the mid 20s, with the cold air flowing in behind the cold front.

Extended Forecast

Things settle down after the storm passes Monday, with mostly clear and dry conditions Tuesday through Thursday. High pressure will dominate, bringing these clear conditions, but also extending the cold snap well into next week as it continues to pump Canadian air into the area. Highs will continue struggling to reach the mid-upper 20s, with overnight lows in the teens at the coast and single digits in the interior.

Interesting note: some of the GFS (Global Forecast System) models are showing the potential development of a strong coastal storm next weekend. Of course, it’s far too early to talk specifics about precipitation type and amounts as this storm may not materialize. The models are fairly consistent in developing a low over the northern Gulf of Mexico, however, a frontal system also develop to be strong enough to push this storm well offshore as it approaches the region.

psu

NYC Weekend Weather Update & CA Storms – Feb 27, 2014

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First up for the NYC area is a bitterly cold end to the work week.

A reinforcing arctic cold front is set to push through the area during the day today, perhaps spurring a few scattered moderate-heavy snow showers. Accumulation, if any, should be light. Behind this frontal boundary, a west wind between 15-20mph will usher in some of the coldest low temps we’ve seen in recent weeks. Lows in the city are forecast to be in the low teens, with zero to single digits in the interior. Wind chill values tomorrow morning will hover around zero.

Friday will be a sunny day with high pressure moving in. Despite the sunshine, temps will struggle into the 20s across the region.

Saturday, a weak frontal system moves through, but with dry atmospheric conditions, little if any snow is expected. Highs will be in the low-mid 30s.

Sunday-Monday, a prolonged winter weather event is forecast. The storm system currently impacting the west coast (see below) will move over the interior of the country, reorganize, and strengthen over the Midwest. This will lead to a stalled cold front draping across our region with multiple low pressure centers to slide along this front. One of these is forecast to develop into a potentially significant coastal storm. Models are coming into agreement that this storm center could pass close to the 40N 70W benchmark sweet spot.

The duration of the storm, starting Sunday night through Monday night means that it could result in significant snowfall, even with possible mixing in with sleet/rain near the coast during the day Monday. Still too early to tell how much snow – will keep monitoring the situation. High temps on Sunday will be in the mid 30s, then drop back into the low 30s for Monday.

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Too much of a good thing for California?

As I noted in earlier posts, and as has been broadcast by the media, California remains in the grips of a crippling drought. A strong pacific storm system is spinning up multiple bands of heavy precipitation during the end of this week. While that is some good news for the drought, the intensity of the rainfall could lead to mudslides, and localized flooding. The best news out of this storm is that elevations over 7000′ are expected to pick up as much as 1-3′ of snow, adding to a paltry snowpack thus far. Check out the graphic from the San Diego NWS station for a look at the heavy rain fall totals expected (5-7″ in higher elevations near the coast with south facing slopes!).

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