015 FXUS65 KTFX 251757 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1145 AM MDT Tue Mar 25 2014 AVIATION SECTION UPDATED .UPDATE... No significant changes to the bulk of the forecast area this morning. Have lowered temperatures across north central and central Montana for this afternoon as cool air continues to be transported into the area by an east wind. Will see some moderation of temperatures throughout the day...however not to the previously anticipated level. Otherwise no significant changes to the forecast. Suk && .AVIATION... UPDATED 1755Z. Axis of high pressure ridge aloft will move across Montana today, with large swath of Pacific moisture crossing thru the ridge to produce widespread high-level ceilings with some scattered mid-level clouds. No precipitation expected over TAF sites in central and southwest MT through this evening, but scattered snow showers and lower ceilings will develop overnight south of a KGTF-to-KLWT line. Could see occasional periods of MVFR conditions vcnty KBZN/KGTF/KLWT early Wed morning. Winds remaining light across the region today. && .PREV DISCUSSION... /ISSUED 545 AM MDT Tue Mar 25 2014/ Today through Thursday...Warmer and drier air moves into the region today associated with the arrival of a strong upper level ridge. Attention now turns to the longwave trough that will bring periods of rain and snow into the state starting early Wednesday. Models have come into general agreement that two separate disturbances will move through as the overall pattern flattens to a more zonal presentation. The first system to arrive early Wednesday is poorly organized. Upper level divergence will support a surface low with a trailing Pacific cold front...causing rain and snow primarily over southwest Montana Wednesday morning. A weak lee trough will develop along the Rocky Mtn Front and briefly support locally gusty winds as this surface low emerges across the mountains. These stronger winds will remain below warning criteria and will occur only for a short time early Wednesday morning. Steep lapse rates over southwest Montana indicate a marginally unstable environment on Wednesday afternoon that could support convective rain or mountain snow showers. A subtle shortwave ridge settles in at mid levels Wednesday night that will suppress...but not likely end overnight precipitation. The next disturbance moves through early Thursday causing more widespread precipitation to resume...again favoring southwest MT. Although initially stronger over the Pacific Northwest...this second wave will weaken while crossing the Rocky Mtns in a confluent upper flow pattern. Both systems will drag a shallow cold front across the Hiline and into north central Montana to maintain cooler temperatures in that area. Details of the timing...coverage and intensity of precipitation will need to refined as the event gets underway. Snowfall should be confined mostly to higher elevations...but may reach the valley floor and areas of the north central plains at night. Nutter Thursday night through Tuesday...Medium range period begins with short wave energy departing the area to the east. Scattered snow will decrease overnight Thursday as weak upper ridging takes place Friday. Because the ridge remains rather flat, enough moisture will push through it resulting in isolated afternoon showers, mainly over the southwest. The flow aloft becomes increasingly southwest on Saturday as a strong upper trof approaches the west coast. Moisture and instability will increase over Southwest Montana with scattered mountain snow showers developing. As the trof axis crosses the Continental Divide Saturday night, and colder air is drawn into the area, the models develop an impressive band of precipitation across North Central Montana with the chances for accumulating snow increasing. This feature is fairly progressive and will push into eastern Montana by Sunday afternoon. Weak upper ridging develops again on Monday allowing drier and warmer conditions to return. Models bring another strong upper trof to the area Tuesday but placement of the main energy core remains in doubt as the GFS keeps it further south than its European counterpart. Temperatures will be near to above seasonal averages as the period begins, with Saturday being the warmest day. Temperatures will be below seasonal averages to start the new week. && .PRELIMINARY POINT TEMPS/POPS... GTF 31 27 42 22 / 0 20 30 40 CTB 32 20 32 17 / 0 30 40 40 HLN 52 31 47 28 / 0 30 40 50 BZN 53 31 46 26 / 0 40 60 60 WEY 48 29 44 23 / 0 50 70 70 DLN 59 32 47 26 / 0 30 50 50 HVR 28 21 37 20 / 0 10 30 30 LWT 43 27 41 22 / 0 10 40 40 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ weather.gov/greatfalls www.twitter.com/NWSGreatFalls www.facebook.com/US.NationalWeatherService.GreatFalls.gov