Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS65 KBOU 242102

Area Forecast Discussion
National Weather Service Denver/Boulder CO
302 PM MDT Sun Sep 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 300 PM MDT Sun Sep 24 2017

Upper low over northeast Utah and slowly weakening and moving
slowly northeast into Wyoming. There is some weak ascent aloft
ahead of the low and this is helping to generate some very light
rain and drizzle over the Front Range and portions of the
northeast plains. This will continue through at least this evening
and most likely continue over the plains through tonight. Expect
the low stratus deck to remain anchored in place tonight and at
least through Monday morning with shallow and moist upslope flow 
in place. The main trof axis will still linger over Western
Colorado through Monday with weak ascent continuing through
eastern Colorado. Subsidence and drying will be moving into the
mountains later in the day. Temperatures will be only slightly
higher than yesterday's readings. 

.LONG TERM...(Monday night through Sunday)
Issued at 300 PM MDT Sun Sep 24 2017

By Tuesday the 500mb Low is progged to be over western North Dakota 
and its weakening upper trough extending back to the Desert 
Southwest. This puts Colorado under a relatively light southwesterly 
mid-level flow. However there's still plenty of cold air aloft with 
the 700-500mb temps over the CWA which should keep sfc temps well be 
average for one more day. Meanwhile, the local airmass becomes drier 
with a shift to a south-southwest low-level flow. However, a shift 
to a slightly wetter southeast sfc flow on the plains, could see 
isolated showers/t-storms forming late afternoon over the srn Front 
Range foothills and South Park area. Overnight and Wednesday, a 
shift to a southerly mid-level flow as an upper low winds up over 
the Desert Southwest will advect increasing amounts moisture up into 
Colorado, some of it reaching the CWA by Wednesday afternoon. Warmer 
temps, increasing QG forcing and a southeasterly/upslope flow will 
increase the chance of afternoon/early evening t-storms specifically 
across the southwest corner of the CWA. Storms will be slow movers 
with light steering winds, but rain amounts will generally be light. 
Except for isolated late day storms on the Palmer Divide, the chance 
for precip on the plains appears quite low. 

By Thursday...models show the Desert SW low lifting newrd over the 4-
corners area, bringing with its a decent amount of moisture. Weak to 
moderate QG forcing in advance of the cyclone expands over the fcst 
area through the day. Furthermore, the GFS indicates a deep easterly 
upslope flow on the plains Thursday, whereas the ECMWF and Canadian 
models show the upslope flow no where as strong. Yet all three 
models indicate areas of light QPF for most of the CWA Thursday 
afternoon and overnight. By Friday, models begin diverging as the 
ECMWF and Canadian models shows the upper low lifting north over 
western WY, the GFS filling the low and opening the trough up over 
Utah and Colorado. The GFS keeps the CWA cool and wet, the Canadian 
models not quite as showery, and the EC cloudy but with lower rain 
chances. Will go with a blend of these sceneries and keep temps 
slightly below average. For the weekend, models show some form of 
this trough passing over the state possibly giving us at least a 
slight chance of showers both days. Although latest temp guidance 
shows temps returning to above average. 


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 300 PM MDT Sun Sep 24 2017

Mainly low stratus deck will remain in place over the terminals 
at least through Monday morning with occasional drizzle through 
this evening. Ceilings will gradually lift Monday afternoon. Surface
winds will remain also light from the east and northeast. 




National Weather Service Glossary of Abbreviations