textproduct: Great Falls

KEY MESSAGES

- Areas of rain continue to circulate across much of north- central Montana through Monday along with breezy to windy conditions and unseasonably cool temperatures.

- Risk for minor flooding is decreasing but some creeks and rivers emanating from the Rocky Mountian Front and Glacier NP will remain elevated through early this week.

- Drier conditions by Wednesday with a late week warming trend but some risk for showers and Thunderstorms Thursday and again next weekend.

DISCUSSION

- Meteorological Overview:

The mid to upper level low that brought widespread and locally heavy precipitation to the area this weekend is currently centered over central/eastern MT and will only slowly lift northward through early this week. There is still a fairly robust plume of deep moisture feeding into this circulation to maintain widespread rain through much of tonight across north-central MT while showers decrease across portions of SW MT south of I-90 through the overnight period. The upper level low circulation does elongate E-W on Monday, allowing for a northward shift of the more widespread area of rain/showers across north-central MT with some drying across the southern half of the forecast area. Most model guidance lifts the circulation center north into southwest SK Monday night through Tuesday, maintaining showers across primarily northern portions of the forecast area before the system eventually moves off to the east Tuesday night.

Gusty northwest winds occurring across north-central MT will also continue through Monday as surface low pressure only slowly shifts north out of northeast MT while a cooler airmass and high pressure continues to build southward from AB behind the the low. This will also keep temperatures below seasonal averages through Tuesday, especially across north-central MT where daytime maximum temperatures remain in the 50s while temperatures moderate closer to seasonal averages by Tuesday across SW MT.

Temperatures warm back to seasonal levels across the entire area on Wednesday and are likely to trend above average Thursday and Friday as a southwesterly flow aloft develops across the region. An upper level wave moves across the Northern Rockies and MT Thursday/Thursday night bringing some showers and thunderstorms with a larger scale trough moving in from the west at some point next weekend bringing additional chances for showers and thunderstorms. Hoenisch

- Forecast Confidence & Scenarios:

There is a 60% or higher probability for additional precipitation amounts of 0.25" or more across much of north-central MT through Monday. A lobe of energy/moisture rotating westward around the low across SK and southern AB Monday will bring higher amounts to Glacier county where there is 60% or higher chance for additional rainfall of 1.00" or more from eastern portions of Glacier NP and east along the AB border.

Will need to watch thunderstorm potential later this week on Thursday and again this weekend with recent moisture providing some added buoyancy and these systems likely to provide adequate wind shear for organized convection. However there is still considerable uncertainty with timing and more There is a 60% or higher probability for additional precipitation amounts of 0.25" or more across much of north-central MT through Monday. A lobe of energy/moisture rotating westward around the low across SK and southern AB Monday will bring higher amounts to Glacier county where there is 60% or higher chance for additional rainfall of 1.00" or more from eastern portions of Glacier NP and east along the AB border.

Will need to watch thunderstorm potential later this week on Thursday and again this weekend with recent moisture providing some added buoyancy and these systems likely to provide adequate wind shear for organized convection. However there is still considerable uncertainty with timing and and more specific details at this time. Hoenisch specific details at this time. Hoenisch

AVIATION

31/18Z TAF Period

There will be rain across all terminals during this TAF Period. At all terminals during at least a portion of this TAF Period there will be MVFR-level ceilings. At the KHLN, KHVR, and KLWT terminals during a portion of this TAF period there is at least a 30% chance for IFR-level ceilings. During the duration of this TAF Period there will be mountain obscuration. At the KWYS terminal if it clears out tonight there is a low chance for fog to form Monday morning. Between 01/00Z and the end of the TAF Period there will be isolated instances of low-level wind shear and mountain wave turbulence. -IG

HYDROLOGY

A Flood Advisory remains in place through this evening to highlight impacts from recent precipitation, including elevated streamflows on creeks near the central MT mountains and Rocky Mtn Front as well as lingering ponding of water in some low-lying areas. These impacts should continue to decrease this evening as precipitation rates remain low (.01-.10"/hr). We will continue to watch several larger creeks/rivers along the Rocky Mtn Front, which are near or forecast to remain close to bankful through Monday. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 41 53 41 58 / 100 80 50 60 CTB 36 45 37 51 / 100 90 90 80 HLN 43 59 42 64 / 90 60 20 40 BZN 37 62 37 67 / 50 30 30 20 WYS 30 62 30 66 / 30 10 20 0 DLN 36 64 38 68 / 20 20 40 10 HVR 39 54 39 61 / 100 90 80 70 LWT 37 55 37 61 / 90 60 30 50

TFX WATCHES/WARNINGS/ADVISORIES

None.