It looks like we’re going to get lucky for Independence Day this year in NYC. While many areas of the Eastern US may see a chance for rain, the Northeast should remain under the influence of strong enough high pressure that we stay dry. That means good news for all the outdoor activities folks have planned coming up! This will be my first detailed forecast that draws on the recently released GFS FV3 forecast model upgrade, so it will be interesting to see how this upgrade performs.
My Forecast
High: 88°F | Low: 74°F | Max sustained winds: 15 mph | Total precipitation: 0.00″ – verification will come from METAR data for the period between 2AM Thursday and 2AM Friday (06Z Thursday to 06Z Friday) at LGA (LaGuardia Airport), and the KLGA Daily Climate Report
Verification
High: 93°F | Low: 71°F | Max sustained winds: 16 mph | Total precipitation: 0.00″ – Spot on with the wind forecast for yesterday. It was a good call to bump that forecast up with possible sea breeze enhancement in the mix. Unfortunately, these winds didn’t do enough to cool temperatures off during the day, and I was off by 5°F for the high temperature. Skies turned out to be pretty much sunny the whole day and while statistical forecast models should factor in urban heat island effects, it would have been prudent to still have forecast at least 90°F in light of this. Also, given the 850 mb relative humidity profile, I should have probably sided with a less cloudy outlook that would have favored warmer high temperatures. Of note, the new GFS model had issues initially with a cold bias that should have been corrected. In this case, it was warm on the low, but too cool on the high. This is worth noting even though these two points of data aren’t necessarily indicative of a trend.
Synoptic Set Up
A stationary front currently along the northern tier of Illinois, Indiana, Ohio, Pennsylvania and western New York will attempt to push northwards tomorrow as a warm front. However, with a 500 mb ridge aloft and an area of surface high pressure over the Northeast and translating over the Gulf of Maine, this frontal boundary is forecast to become stationary, holding just southwest of the NYC metro area. Moisture above the surface looks modest, and without any impulses of low pressure at the surface or troughs aloft, there doesn’t appear to be any support for precipitation.
High Temperatures
GFS, NAM, and NBM agree that July 4th a warm day. All three statistical models come in at between 88-89ºF for high temperatures. EKDMOS (ensemble MOS) 50th percentile matches is very close, at 87-88ºF. The only hitch to warm temperatures is that NAM shows the possibility for low clouds and wind directions are forecast to veer from east-northeast to southeast. Cloud cover could eat into temperatures rising too much, and winds coming from the directions indicated would bring a cooling influence of marine air with sea surface temperatures still in the low-60s at this point in the season. With these factors in mind, but also keeping in mind the effects of the urban heat island, I’ll side with a middle of the road forecast of 88ºF.
Low Temperatures
NAM and GFS MOS both show the chance that the low temperature during this forecast period may actually fall overnight going into Friday. Either way, both are very close showing lows ranging 73-75ºF. EKDMOS 50th percentile shows 74-75ºF for the low. Increasing cloud cover should stall any serious radiational cooling, and there’s little indication of any temperature advection either way with weak winds. I’m again going with the mean here and siding with a forecast of 74ºF for the low.
Max Sustained Winds
NAM, GFS, and NBM average out to 8 knots for the max sustained wind tomorrow. EKDMOS is more aggressive with winds in the 50th percentile about 13-15 knots. While forecast soundings don’t show too much evidence to support a forecast above 10 knots since the entire wind profile looks remarkably calm for tomorrow, this same tendency to weak synoptic winds could allow for a fairly robust sea breeze to develop, and this could be the what allows sustained winds to top 10 knots. I’ll go with the low-end of the EKDMOS and call for 13 knots (15 mph).
Total Precipitation
High pressure is forecast to be in control, with a 500 mb ridge in place. There aren’t any frontal boundaries moving through to create lift and even if there were, there simply isn’t enough moisture to support precipitation. Both the forecast sounding above and 850 mb forecast for relative humidity and winds below show moisture values that are insufficient to bring about any precipitation.
