Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 191039
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
439 AM MDT TUE MAY 19 2015

.SHORT TERM...VALID FOR TDY AND WED...

WEAK RIDGING EXISTS OVER MT AS UPPER LOW MOVES SLOWLY THROUGH THE
GREAT BASIN...WITH A 90KT H3 JET OVER AZ/NM. THIS JET WILL NOSE
INTO THE CENTRAL PLAINS TODAY AS THE MID LEVEL LOW LIFTS INTO WY.
COMBINATION OF STRONG/DRY RIDGING JUST TO OUR NORTH AND SHORTWAVE
ENERGY DROPPING FROM CANADA INTO THE NORTHERN PLAINS WILL LARGELY
SUPPRESS MOISTURE ASSOCIATED WITH THE LOW TO OUR SOUTH. FORCING
ALONG BAROCLINIC ZONE WILL ALSO STAY TO OUR SOUTH WITH GREATEST
PCPN EXPECTED TO OCCUR OVER WY/NE/SD. ALL OF THIS BEING SAID...WE
SHOULD STILL SEE SOME LIGHTER PCPN WORK INTO OUR SOUTHERN TIER
THIS AFTERNOON AND TONIGHT...WITH A TAPERING OFF BY WEDNESDAY AS
ENERGY SHIFTS EAST. WILL KEEP OUR NORTH DRY AND CHANCE/LIKELY POPS
ACROSS OUR SOUTH. PCPN WILL BE HEAVIEST IN UPSLOPE AREAS OF OUR
SOUTH... IE THE BIGHORNS AND THEIR EASTERN FOOTHILLS...WITH MAYBE
A TENTH TO QUARTER INCH OF MOISTURE IF IT MAKES IT THIS FAR NORTH.
OVERALL HAVE FOLLOWED THE 03Z SREF WHICH SHOWED A DISTINCT
SOUTHWARD/DRIER TREND AND IS GENERALLY CONSISTENT WITH THE GFS/
ECMWF. HAVE REDUCED POPS ACROSS THE CWA ON WEDNESDAY AS THE
SHORTWAVE EXITS AND IS FOLLOWED BY ONLY WEAK DIURNAL CONVECTION
OVER OUR SOUTHERN MTNS AND FOOTHILLS. AREAS FROM HARLOWTON TO
ROUNDUP...MILES CITY AND BAKER WILL STAY DRY OVER THE NEXT COUPLE
DAYS...BILLINGS WILL SEE NOTHING MORE THAN A FEW SPRINKLES.

GRADUAL WARM UP IS ON TAP TODAY AND WEDNESDAY WITH TEMPS REMAINING
BELOW NORMAL. THIS IS COURTESY OF PERSISTENT EASTERLY FLOW DRAWING
COOLER AIR FROM HIGH PRESSURE ANCHORED OVER THE NORTHERN PLAINS.

JKL

.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...

THURSDAY IS A TRANSITION DAY AHEAD OF ANOTHER SYSTEM MOVING INTO
CENTRAL CALIFORNIA. FLOW ALOFT WILL BE WEAK BUT MOISTURE OVER THE
MOUNTAINS SHOULD BE SUFFICIENT FOR SHOWER ACTIVITY WITH A BIT OF
MOVEMENT INTO THE ADJACENT PLAINS. EASTERLY SURFACE FLOW STAYS IN
PLACE FOR CONTINUED BELOW NORMAL TEMPERATURES.

FRIDAY SEES A WEAK WAVE EJECTED BY THE UPSTREAM TROUGH MOVING
THROUGH THE AREA WHICH WILL GENERATE BETTER COVERAGE OF SHOWER
ACTIVITY. ADDED ISOLATED THUNDER TO THE AFTERNOON AND EVENING
TIME PERIOD FROM THIS TIMEFRAME THROUGH THE REST OF THE FORECAST
PACKAGE. SATURDAY LOOKS SIMILAR TO FRIDAY BUT WITH A BIT MORE
MOISTURE IN THE AREA BUT STILL RELATIVELY WEAK FLOW ALOFT.
TEMPERATURES WILL BE BELOW NORMAL WITH EASTERLY FLOW ON FRIDAY
WITH THE WINDS TURNING NORTHERLY ON SATURDAY IN RESPONSE TO
PRESSURE FALLS OVER WYOMING.

THESE PRESSURE FALLS ARE A RESULT OF THE WEAKENING CALIFORNIA
SYSTEM MOVING INTO WYOMING THOUGH THE ECMWF IS CONSIDERABLY WEAKER
THAN THE GFS. GFS IS THE MUCH WETTER SOLUTION FOR SUNDAY AND THERE
IS AGREEMENT BETWEEN THE GFS AND CANADIAN MODELS WHILE THE ECMWF
IS FASTER WITH THE WEAKENING OF THIS SYSTEM. HAVE TRENDED
PRECIPITATION CHANCES HIGHER TO MAKE SURE THEY ARE ABOVE
CLIMATOLOGY FOR SUNDAY AND WILL WAIT TO SEE HOW WET THE MODELS
MAKE THE LATTER PART OF THE WEEKEND. BEGINNING OF NEXT WEEK LOOKS
UNSETTLED WITHOUT ANY WARMUP EXPECTED. BORSUM

&&

.AVIATION...

LIGHT WINDS THROUGH THE PERIOD WITH MID LEVEL CLOUDS MOVING INTO
THE REGION FROM THE SOUTH. KLVM WILL SEE STRATUS OVERNIGHT WITH
MVFR CEILINGS BUT VFR CONDITIONS EXPECTED AT OTHER TERMINAL
SITES. EXPECT VFR CONDITIONS AT KLVM BY MID MORNING. ISOLATED
SHOWER ACTIVITY WILL MOVE INTO THE MOUNTAINS DURING THE AFTERNOON
HOURS POSSIBLY REACHING KSHR. BORSUM
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY WED     THU     FRI     SAT     SUN     MON
-------------------------------------------------------
BIL 057 039/060 040/067 043/070 045/067 046/062 045/068
    1/E 10/B    01/B    12/T    33/T    33/T    33/T
LVM 052 037/056 038/064 040/067 042/064 043/061 041/064
    2/W 21/N    12/T    23/T    44/T    43/T    44/T
HDN 059 037/062 037/069 043/072 044/070 046/064 045/071
    1/E 21/B    11/B    12/T    33/T    33/T    32/T
MLS 062 036/063 038/068 044/069 046/066 047/062 046/068
    0/B 00/B    00/U    02/T    22/T    34/T    42/T
4BQ 052 035/058 036/065 042/066 044/065 047/061 044/066
    3/W 32/W    10/B    12/T    23/T    44/T    42/T
BHK 059 033/060 034/066 040/065 043/061 044/060 042/064
    0/U 00/U    00/U    02/W    22/T    34/T    42/T
SHR 050 034/055 035/062 040/064 041/064 043/060 041/065
    5/W 52/W    11/B    23/T    34/T    44/T    43/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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