Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240441
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1041 PM MDT SAT MAY 23 2015

.DISCUSSION...

TONIGHT...SHOWERS HAVE BEEN DIMINISHING THROUGH THE EVENING AND
ALMOST ALL LIGHTNING ACTIVITY HAS CEASED. UPDATED TO FRESHEN FIRST
PERIOD POPS, QPF, WX, AND WINDS. ZELZER

&&

.AVIATION...UPDATED 0438Z.

THE AIRMASS IS UNDER THE INFLUENCE OF A BROAD UPPER LEVEL LOW
PRESSURE SYSTEM. THE REMAINING SCATTERED SHOWERS AND A FEW
THUNDERSTORMS ASSOCIATED WITH THIS SYSTEM ARE NEAR KGTF AND KHLN.
LOCAL MVFR CONDITIONS ARE POSSIBLE NEAR SHOWERS AND THUNDERSTORMS.
ALSO, SOME IFR CONDITIONS ARE POSSIBLE TOWARDS SUNRISE DUE TO LOW
CLOUDS AND FOG. VFR CONDITIONS WILL PREVAIL THROUGH THE REMAINDER OF
SUNDAY.

&&

.PREV DISCUSSION...
/ISSUED 540 PM MDT SAT MAY 23 2015/
ANALYSIS SHOWS BROAD, SLOW-MOVING LOW PRESSURE SYSTEM, CURRENTLY
CENTERED OVER EASTERN UTAH, CONTINUING TO BRING MIX OF GULF OF
MEXICO AND PACIFIC MOISTURE INTO CENTRAL/SOUTHWEST MT. THE ABUNDANT
MOISTURE AND SLIGHTLY UNSTABLE CONDITIONS HAVE LED TO ANOTHER ROUND
OF SCATTERED SHOWERS AND ISOLATED, SHORT-LIVED THUNDERSTORMS ACROSS
MUCH OF THE REGION THIS AFTN, WITH CONVECTIVE ACTIVITY EXPECTED TO
CONTINUE THROUGH THE EVENING HOURS, THEN DISSIPATE TOWARD SUNSET
THOUGH SOME SHOWERS WILL LINGER FROM HELENA TO DILLON OVERNIGHT.
FORECAST MODEL SOLUTIONS HAVE VARIED LITTLE OVER LAST SEVERAL RUNS,
GIVING GOOD CONFIDENCE THAT THE LOW PRESSURE SYSTEM WILL STAY ON ITS
NORTHEAST COURSE AND REACH EASTERN WYOMING BY SUNDAY NIGHT. THIS
TRACK WILL ALSO MOVE MOST OF THE ACCOMPANYING MOISTURE INTO EASTERN
MT, BRINGING DRYING CONDITIONS FROM GREAT FALLS NORTH TO THE US/CAN
BORDER, WHILE SCATTERED SHOWERS CONTINUE ALONG/SOUTH OF A LINE FROM
LEWISTOWN TO DILLON. MEMORIAL DAY FORECAST STILL LOOKING MOSTLY DRY
ACROSS THE REGION AS WEAK HIGH PRESSURE RIDGING SLIDES ACROSS THE
STATE AHEAD OF THE NEXT SHORTWAVE TROF THAT MOVES INTO WA/OR ON MON.
SHOWERS AND A FEW THUNDERSTORMS WILL DEVELOP ALONG THE ROCKY MTN ON
MON AFTN/EVE AND EXPAND EASTWARD TO THE INTERSTATE 15 CORRIDOR BY
MON EVE. AS FOR TEMPERATURES, THE EXITING LOW PRESSURE SYSTEM AND
MOISTURE WILL RESULT IN DECREASING CLOUD COVERAGE FOR LATTER HALF OF
THE HOLIDAY WEEKEND, ALLOWING AFTN HIGHS TO CLIMB INTO THE MID- AND
UPPER 60S TOMORROW AND LOW 70S ON MON.
WARANAUSKAS

MONDAY NIGHT THROUGH SATURDAY...THE LATEST GFS AND ECMWF MODEL RUNS
ARE IN BETTER AGREEMENT IN THEIR HANDLING OF AN UPPER LOW THAT IS
OVER WASHINGTON MONDAY NIGHT. THE GFS MOVES THE UPPER LOW VERY
LITTLE INTO TUESDAY NIGHT WHILE THE ECMWF WEAKENS THE UPPER LOW AS
IT MOVES VERY SLOWLY EAST. BY THURSDAY BOTH MODELS HAVE AN UPPER
TROUGH OVER WESTERN MONTANA THROUGH SOUTHERN IDAHO. DUE TO THIS
BETTER AGREEMENT HAVE RAISED CHANCES OF PRECIPITATION THROUGH
MIDWEEK AND ESPECIALLY TUESDAY OVER THE WESTERN MOUNTAINS THROUGH
SOUTHWEST MONTANA. LATER IN THE WEEK THE ECWMF IS FASTER MOVING THE
UPPER TROUGH EAST AND HAVING AN UPPER RIDGE MOVE OVER WESTERN
MONTANA. BY SATURDAY THE GFS STILL HAS THE UPPER RIDGE OVER IDAHO.
THESE DIFFERENCES LEAD TO THE ECMWF BEING RELATIVELY DRIER THAN THE
GFS. DUE TO THE DIFFERENCES WILL CONTINUE WITH THE IDEA OF
PRECIPITATION RANGING FROM BEING SCATTERED OVER SOUTHWEST MONTANA TO
ISOLATED TOWARDS THE U.S. ROUTE 2 AREA. HIGH TEMPERATURES ARE
EXPECTED TO CHANGE LITTLE FROM DAY TO DAY DURING THE 5 DAY PERIOD.
BLANK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  44  66  43  71 /  20  20  10  10
CTB  39  69  39  70 /  20  10   0  10
HLN  46  67  44  73 /  30  20  10  20
BZN  41  61  39  68 /  40  30  30  20
WEY  33  57  32  61 /  50  20  20  30
DLN  44  62  40  68 /  20  20  20  30
HVR  41  72  43  74 /  10  10  10  10
LWT  43  61  42  67 /  10  30  30  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

WEATHER.GOV/GREATFALLS


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