Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
738 FXUS65 KBOU 150213 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 813 PM MDT Sat Sep 14 2024 .KEY MESSAGES... - Dry today and tonight with temperatures above seasonal normals. - Scattered showers and isolated thunderstorms Sunday afternoon and evening with gusty outflow winds and only light to briefly moderate rainfall. A stronger storm possible far northeast plains. - Fire weather conditions get elevated to locally critical again next week with the worst fire weather conditions being on Tuesday and Thursday. - Cooler temperatures and the potential for precipitation expected for the latter half of next week. && .UPDATE... Issued at 805 PM MDT Sat Sep 14 2024 Radar and satellite paint a quiet picture across the forecast area this evening. One lone supercell in the Nebraska panhandle this afternoon did briefly contemplate a motion towards the CO border, but quickly decided to simply dissipate instead. In the meantime, temperatures have decreased back to a value that I find tolerable, and overnight lows should be near to a little above normal. Didn`t have to make any significant adjustments to the forecast grids overnight, as the previous forecast was in good shape. One remaining question is if any fog does form across the far northeast corner towards tomorrow morning. Some deterministic hi- res guidance does develop some fog, but BUFKIT profiles at STK/AKO would favor mist or perhaps patchy low stratus for a few hours before it quickly burns off. && .SHORT TERM /Through Sunday/... Issued at 135 PM MDT Sat Sep 14 2024 Temperatures have made it into the mid and upper 80s across the urban corridor this afternoon. With a few more hours of surface heating to go, these should climb a few more degrees. Mostly clear skies are expected overnight tonight that will allow temperatures to cool into the low 50s across the plains, 40s for the foothills and Palmer Divide, and 30s for the mountains. Conditions are expected to remain dry, however, one area to note is the far northeastern plains where dewpoints remain in the 60s. The SPC meso analysis currently shows 1500-2000 J/kg of MLCAPE in this area. Forecast soundings keep this capped through the evening, but if the cap were to break, we could end up with a slight chance for thunderstorms developing. Have kept a slight chance in the grids to account for this. For Sunday morning, low dewpoint depressions and light winds are expected across the far eastern plains before sunrise, which could initiate fog formation. The hi-res Grand Ensemble indicates a 30-50% chance that visibility will drop to less than .5 miles for a few hours in the morning from Weld County east across the state. Added areas of patchy fog to account for this. Ensembles show an uptick in mid-level moisture tomorrow afternoon, mainly for the high terrain with the GFS/ECMWF indicating PW anomalies of 115-155% of normal. Inverted V forecast soundings translate to afternoon high-based showers initiating across the high country. Guidance show potential for outflow winds to gust to 50 mph in areas where showers/storms develop. Marginal instability is expected across the majority of the CWA, with the exception of the northeastern plains. However, forecast soundings continue to portray a capped environment, but if the cap were to break, we could see some stronger storms develop, especially for this time of year. Above normal temperatures are expected to continue, climbing a degree or two warmer than today. && .LONG TERM /Sunday night through Saturday/... Issued at 135 PM MDT Sat Sep 14 2024 Southwesterly flow aloft will be over Colorado on Monday with diffluence in the upper level jet streak. A shortwave trough will begin moving toward Colorado throughout the day with a slight increase in QG ascent. At the surface, moderate southerly winds will develop across the plains with lee cyclogenesis developing over Montana. Soundings show the low levels will be rather dry so only isolated showers and storms will form mainly over the higher terrain. Gusty winds will be possible out of these storms due to large DCAPE values. Otherwise, there will be warm temperatures with a high around 90 in Denver. That is well above the normal high of 80 but not within reach of the record high of 95. The axis of the shortwave trough will move through our forecast area by late Tuesday. There will be moderate QG ascent due to PVA and this forcing may create a line or two of showers and storms. Some model solutions like the Canadian are rather wet with most ensembles showing some rain falling across the majority of the area. However, the ECMWF is drier and with southwesterly flow at the surface, the drier solution seems more likely at this moment. PoPs were kept on the low side as a result. The strong southwest winds may gust up to 40 mph across the plains. With the warm, windy, and dry conditions, there may be some areas that approach critical fire weather conditions. There will be subsident flow on the backside of a departing trough on Wednesday will result in dry weather. Cooler temperatures aloft will transition to the surface with highs being about 5 F cooler than Tuesday. Highs will still be above normal. Another shortwave trough will be quick on the heels of the first one. It will arrive in Colorado on Thursday and into Friday and will provide QG ascent. There are many different solutions within the ensembles for the evolution of this trough. Some have a quicker-moving trough that is more positively tilted. In that scenario, there may be a brief chance of rain across our forecast area but light amounts would be expected. There are also plenty of solutions with a slower, more negatively tilted trough. This would be a much wetter scenario and some of these solutions have over an inch of rain in Denver. It is still too early to have an idea of which solution is more likely but climatology seems to favor the drier solution. && .AVIATION /00Z TAFS through 00Z Monday/... Issued at 531 PM MDT Sat Sep 14 2024 Easterly winds this afternoon will gradually turn back towards typical drainage flow this evening and early overnight. High-based showers are possible on Sunday afternoon, leading to a more complicated wind forecast. Generally expecting a turn back to the east or southeast tomorrow, but gusty outflow winds will likely be an issue at times after 20-21z. Could see a few gusts up to 35-40kt with stronger microbursts. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hiris SHORT TERM...Bonner LONG TERM...Danielson AVIATION...Hiris