textproduct: Glasgow

KEY MESSAGES

- Fog north of the Missouri River and near the Yellowstone Valley will clear by mid to late morning.

- Warmer than average temperatures will persist through Tuesday.

- An approaching upper-level trough will produce decreased temperatures and chances for precipitation beginning Wednesday.

DISCUSSION

A high-pressure system over the northern Midwest is producing southeasterly surface winds across the northern Great Plains, resulting in moisture pooling in northeast Montana. The lack of solar heating associated with the ongoing transition to winter is significantly limiting atmospheric mixing, resulting in an inversion over the region. The inversion, coupled with the aforementioned moisture pool, is resulting in fog across northeast portions of the state.

Fog this morning-- like the past couple mornings-- is difficult to forecast exactly. However, Daniels, Sheridan, Roosevelt, and northeast Valley Counties will likely see fog clear by mid-morning. Fog near the Yellowstone valley is anticipated to clear by late morning.

Fog aside, an upper-level ridge over Montana will result in warmer than average temperatures through Tuesday.

The ridge will eventually exit eastward ahead of an upper-level trough that will dig over Montana by Wednesday, resulting in temperatures dropping significantly and returning to near seasonal averages.

Moisture-ladden southwesterly flow aloft associated with the trough will enable precipitation starting Wednesday. At this time, the predominant mode is expected to be rain as opposed to snow. Confidence will improve as time progresses.

FORECAST CONFIDENCE & DEVIATIONS:

- Added fog in regions surrounding the Yellowstone Valley. No further deviations from the NBM were made.

- Confidence in fog placement and visibilities this morning is moderate (60%). - Confidence in fair conditions persisting through Tuesday is high (85%).

- Confidence in mid-week trough timing is moderate to high (75%).

- Confidence in precipitation mode and amounts next week is low (20%).

DON

AVIATION

LAST UPDATED: 0730Z.

FLIGHT CAT RANGE: VFR - LIFR

DISCUSSION: Low-level ceilings at all stations have the chance (30-50%) to induce IFR conditions by early morning-- if they haven't already. The northern terminals, KGGW and KOLF, have the chance (15-30%) to develop LIFR conditions due to ceilings below 500 feet between 13Z and 17Z. Ceilings will lift and scatter out by early afternoon.

Current NBM guidance indicates fog will likely stay north of KGGW and KOLF, but there is still a significant-- albeit uncertain-- chance (40-70%) that it creeps far enough south to impact these stations. Similarly, Morning fog around the Yellowstone Valley has the chance to impact KGDV, but uncertainty is to great for inclusion in any TAFs.

WIND: E-SE at 08 to 14 knots with gusts up to 24 knots, decreasing to 05 to 10 knots by mid-morning.

GGW WATCHES/WARNINGS/ADVISORIES

None.