textproduct: Missoula
This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.
DISCUSSION
KEY MESSAGES:
- High Pressure to bring prolonged dry pattern next 7-10 days.
- Risk for light freezing rain event across Lincoln County late Sunday night into Monday morning.
Confidence is high for a prolonged period of relatively mild and dry conditions across the Northern Rockies for the next 7-10 days. Global ensembles are in strong agreement for a high amplitude ridge of high pressure to remain anchored along the U.S. West Coast, with the storm track positioned well to the north. Mild temperatures are expected across the midslopes and mountain areas, while valleys continue to experience inverted conditions. Valley fog and stratus have been isolated thus far and this trend will continue into Monday as waves of mid-upper level cloud cover stream in from the north-northwest. This cloud cover will reduce overnight radiational cooling, disrupting the development of widespread stratus and fog.
The main period to watch for notable weather impacts is late Sunday night into Monday morning. Models suggest Lincoln and Flathead Counties in Northwest Montana will be on the southern most extent of a plume of Pacific moisture moving across southern Canada. Models have been trending downward with precipitation amounts the last few days with this feature, with forecast amounts of a trace to 0.03 inches in the valleys and up to 0.20 inches in the higher terrain. Nonetheless, with inversions in place and snow levels forecast to rise near 5,000-6,000 feet, light freezing rain is a concern, mainly focused for areas north of US-2 and west of US-93 in Lincoln County.
The ridge axis will shift further eastward Tuesday into Wednesday. Stagnant conditions will help to strengthen valley inversions, increasing the risk for areas of fog and stratus.
AVIATION
Valley inversions will continue through Sunday. Expect VFR conditions for most locations. Drier surface conditions and waves of mid-upper level cloud cover will help to reduce the development of widespread valley fog and stratus. Isolated areas of fog will develop near bodies of water and rivers, with a 10-20% chance for periods of visibility below 2SM for KGPI and KMSO through 11/1600Z.
MSO WATCHES/WARNINGS/ADVISORIES
MT...None. ID...None.
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