Marine Weather and Tide Forecast for South Glastonbury, MT

DISCUSSION
Through Monday Night...

Satellite imagery shows a deepening trof over the Pacific coastal states with mid level flow backing to the southwest across the Rockies. This pattern is inducing easterly low level winds across the plains which may be producing some capping effect, but some weak forcing from diffluence and height falls is developing in SW Montana with some showers popping up in our far western zones.
This trend will continue with any convection tracking north as southerly flow strengthens this evening, thus keeping the bulk of any precipitation over the western half of our CWA, mainly from Yellowstone County westward this evening. CAPE is modest (<500 J/kg) and shear weak, so we are not expecting any strong strong thunderstorms within this activity.

Surface low develops overnight into Sunday across north central Wyoming with an inverted surface trough extending north (Sheridan to east of Roundup). Expect to see showers/some thunder with cooler conditions on west side of this inverted trough, and a warm sector under it over the Big Horns into south central Montana.
MUCAPE values push 750-1000 J/kg across the Big Horns into SE MT by early afternoon. As heights falls and cooler air slowly push east, there are hints of some stronger convection developing in this warm unstable sector with strong low level convergence.
Convective feedback with PWATS around 0.80 inches suggest heavy rain (and possibly some small hail) is possible with some of the scattered to numerous storms that develop. Thus, the Flood Watch over the Big Horns region, where saturated ground is likely to be found, still looks prudent for tomorrow.

As a complex pattern evolves over the region Sunday night into Monday (deep cyclonic flow with two lows pin-wheeling around from the Great Basin to the Nebraska panhandle). This will produce areas of moderate to heavy rainfall over our CWA, and possibly some periods where areas get dry slotted. Ensembles continue to show a great deal of spread in placement and amounts of precipitation, but are consistently hitting the Big Horns north to the Snowies with 1 to 1.5 inches of rainfall through the event. The Big Horns area has the best chance (30%) of seeing up to 2 inches of liquid through Monday. Thus, the Flood Watch looks good to go through Monday in this area.

The upper trough complex eventually moves out into the central plains by Monday evening with rainfall decreasing from west to east over our forecast area.

A few other items...Pressure falls in our central zones on Sunday will allow for increasing SE winds over our east, strongest near the Dakotas line. Current indications are for 40-50 mph gusts from Baker to Ekalaka. There is a 50-70% chance of gusts reaching 50 mph in this area. Snow levels will initially be over 9000 ft Sunday, but fall to around 6500 ft in the Beartooths by Monday and to around 7000 ft in the Big Horns by Monday afternoon. Thus, the high country may see some decent wet snowfall with 5-10 inches possible over the higher Beartooths, and 4-8 inches possible in the higher Big Horns. Next couple of shifts will monitor for winter highlights, but for now there is much uncertainty with snowfall (ensembles range from 1 to 7 inches for Burgess Junction).

Temps on Sunday will max out in the mid 50s west to lower 70s central and east, warmest in an area from Billings-Sheridan to Miles City-Broadus. BT

Tuesday through Saturday...

Into Tuesday, the upper level low will depart to the east, bringing precip chances to eastern MT. Ensembles have the next shortwave coming into the west Tuesday evening through Wednesday.
There is still disagreement in precip amounts, but there is a low to moderate chance for a quarter inch of precip through Wednesday night. Additional disturbances will pass through Thursday and for the weekend with the weekend system looking more promising as far as moisture. In short, conditions will remain unsettled through next week with daily precipitation chances. High temperatures will be around average with highs in the upper 50s to low 70s. TS

AVIATION

Scattered showers with a few thunderstorms will develop this afternoon and evening. A small chance (20%) of thunderstorms is mainly for KLVM. Breezy SW winds will ramp up late this evening for SE MT (KMLS) with gusts of 25-35 kts through Sunday. TS

PRELIMINARY POINT TEMP/POPS

Sun Mon Tue Wed Thu Fri Sat ----------------------------------------------------------- BIL 050/065 045/052 042/066 043/066 046/070 047/069 048/069 29/T 97/W 45/W 53/T 25/T 43/T 34/T LVM 045/054 035/058 038/061 037/064 041/067 041/068 043/064 5+/T 64/W 26/W 62/T 25/T 33/T 34/T HDN 050/070 043/050 040/064 041/066 044/071 045/070 046/070 29/T +8/W 55/W 54/T 25/W 44/T 44/T MLS 048/068 044/050 041/059 040/065 043/071 047/068 047/071 25/T +9/W 75/W 34/W 24/W 43/W 43/W 4BQ 047/069 043/046 040/058 039/063 043/071 046/068 047/070 16/T 99/W 74/W 33/T 13/W 43/T 33/T BHK 041/056 038/046 035/052 035/061 037/068 043/066 043/067 24/T 99/W 86/W 43/W 23/W 43/W 32/W SHR 044/069 038/047 037/062 036/062 039/072 041/069 043/070 18/T +9/W 55/W 55/T 14/T 34/T 34/T

BYZ WATCHES/WARNINGS/ADVISORIES
MT...Flood Watch in effect from Sunday afternoon through Monday afternoon FOR ZONES 138-169-171.
WY...Flood Watch in effect from Sunday afternoon through Monday afternoon FOR ZONES 198-199.