Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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
422 FXUS63 KFGF 212340 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 640 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - There is potential for localized frost in portions of west- central Minnesota Sunday night into Monday morning. && .UPDATE... Issued at 640 PM CDT Sat Sep 21 2024 Most CU is transitioning east or dissipating with the setting sun, and winds are on the expected downward trend. Very dry air arrives with the northwest flow aloft, so while radiational conditions are good, there isn`t a signal for fog development. Shallow/ground fog may still develop near sunrise Sunday, but impacts are highly uncertain/limited. Guidance doesn`t support adding fog at this time, so I held off with this update. There are no other changes from previous forecast/discussion. && .DISCUSSION... Issued at 241 PM CDT Sat Sep 21 2024 ...Synopsis... Post cold frontal, continental air mass is infiltrating the Northern Plains with surface high pressure building into the region from the northwest. This is bringing in drier air with closer to average temperatures for this time of year. Winds decrease around sunset this evening, with calm and clear conditions tonight promoting some ground fog Sunday morning. Although a lack of higher moisture content should prevent more widespread chance for dense fog. Surface high pressure moves into Minnesota late Sunday into Monday. This may help bring some localized frost to some areas in Minnesota late Sunday night into Monday morning. Quasi-zonal flow aloft with progressive shortwave trough early next week will bring a period of breezy winds, but lack of moisture keeps dry conditions favored. Mid to late week, anomalously strong upper ridging builds into the Intermountain West and Canadian Prairies. This will eventual lean into the Northern Plains and Upper Midwest, promoting another period of above average temperatures at least into the 70s and 80s. As this ridging builds, continued lack of moisture and forcing for ascent will keep conditions dry. ...Sunday Night Frost Potential... Dry air mass comprised of dew points into the mid to upper 30s will overspread the region Sunday night into Monday. Surface high pressure will be migrating into Minnesota by this time, with a increasing surface pressure gradient and cloud cover from the west into North Dakota and Red River Valley SUnday night. Areas that can remain calm and clear to mostly clear hold the chance of efficient radiational cooling, bringing temperatures below 40, and potentially to the mid 30s. Current guidance presents areas within west-central Minnesota hold potential for localized frost conditions Sunday night into Monday morning. Uncertainty in whether or not this happens (and more precise locations) stems from differences in guidance with respect to cloud cover and surface winds. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 640 PM CDT Sat Sep 21 2024 VFR conditions should prevail through the TAF period as CU dissipates with the setting sunset and much drier air arriving in northwest flow. Gusty winds northwest winds are already decreasing, and the approach surface high pressure and loss of mixing should result in light and variable if not calm winds later tonight/Sunday morning. Clearing skies/light winds do raise the potential for patchy fog, but the amount of dry air immediately off the surface (and no guidance highlighting development) lowers confidence in impacts/coverage. Surface gradient remains weak through the day Sunday, with dry air aloft. Prevailing winds should increase with mixing in the west-northwest direction (6-10kt) for most locations and there is a a low chance for 5000 FT AGL CU redeveloping in northeast ND (ceiling development unlikely). && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...DJR DISCUSSION...CJ AVIATION...DJR