Daily Archives: October 3, 2018

WxChallenge for Portland International Airport (KPDX) | Oct 2-5

Last Week’s Results

After the first week of the WxChallenge (and part of this week), I’m second place in my class, tied with multiple others for #268 nationwide, and a little better than national consensus with 21.2 error points. I got hit the last day for going over on temperatures and winds, and will discuss that below. Hats off to one of my classmates who’s currently #44 nationwide!

Verifications

Below are the verified readings for each metric we were asked to forecast during last week, and a column showing error points I was assessed.

Forecast Day Max Temp (°F) Min Temp (°F) Max Sustained Wind (kts) Precipitation (inches) Error Points Assessed
09/25/2018 82 50 11 0.00 4.0
09/26/2018 83 52 11 0.00 1.0
09/27/2018 84 52 9 0.00 2.5
09/28/2018 86 53 11 0.00 6.5

Post-Mortem

Day 1: went too aggressive on the max winds, and too warm on the low temps. The lower winds could explain the lower min temps (less mixing on clear nights). I think I was too optimistic about the possibility of funneling of winds from the ENE along the Columbia River Gorge.

Day 2: did pretty well, only got 1 point off for missing the high temp slightly. If I had stayed with my original forecast for that I would have had a perfect score! Much better on winds though.

Day 3 & Day 4: another decent day, but went a little too cool with the low temperatures. This low bias also bled into Day 4, where I was low on both the high, low, and max sustained wind speeds. I think if I were to go back and redo this, maybe I would have used the Delta Method (a form of moderate persistence) and been better off than looking at MOS, given how stable conditions were throughout the week.

Forecasting for KPDX October 2-5, 2018

Synoptic Set Up

Big changes in store for Oregon in the second week of the forecast challenge. The rex block and high pressure that brought a week of above normal warmth and clear skies last week will finally break down. The upper low associated with it will move northeast towards KPDX over the weekend. Local NWS forecasters currently (as of Thursday) noted considerable spread in forecast guidance about phasing of northern stream energy and a second upper low by the beginning of this forecast period, as well as interaction with outflow from Hurricane Rosa. AFD mentions longwave troughing as well, and this is backed up by GFS progs.

Rainy start to the week at KPDX possible
Coastal low coming ashore on Friday at KPDX

 

Forecast Rationale

The effects of the synoptic set up favor much cooler and unsettled conditions compared to last week. A drop in 500 mb heights with upper lows and longwave trough should result in temperatures close to or slightly below climatological norms. The prospect of this troughing means that precipitation will be in the mix as well at the start of the week. More substantial rain chances are in store for KPDX to end the week. Along with the rain Friday, we can expect cooler temperatures and windy weather as rain cooled air helps mix down some momentum from the lower atmosphere.

Forecasts Submitted

This only reflects finalized forecasts as of this posting, I’ve made small adjustments to the forecast based on checking MOS daily.

Forecast Day Max Temp (°F) Min Temp (°F) Max Sustained Wind (kts) Precipitation (inches)
10/02/2018 68 54 11 0.05
10/03/2018 67 45 7 0.00
10/04/2018 66 46 7 0.00
10/05/2018 57 49 15 0.28