Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 220345 AAB
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
945 PM MDT MON JUL 21 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH WEDNESDAY...

SENT ANOTHER UPDATE TONIGHT TO INCREASE POPS ACROSS OUR NORTH
CENTRAL ZONES AS THOSE RAIN SHOWERS HAVE HELD TOGETHER LONGER THAN
ANTICIPATED IN THE MODELS. MAY BE A CHANCE FOR A FEW LIGHTNING
STRIKES THERE BUT NOT MUCH IS EXPECTED. SHOWERS OVER THE SOUTHERN
ZONES HAVE DISAPPEARED. DECIDED TO REMOVE THEM FROM THE GRIDS
ACCORDINGLY. BMICKELSON

SENT AN UPDATE TONIGHT TO PROVIDE MORE DETAIL TO THE GRIDS
FOLLOWING RECENT RADAR REFLECTIVITIES...SATELLITE IMAGERY...AND
LATEST MODEL DATA. NOT MUCH LIGHTNING IN THESE STORMS. CUT BACK ON
THAT WORDING AS WELL. OVERALL PRECIP IS EXPECTED TO DIMINISH
THROUGH THE NIGHT TONIGHT. BMICKELSON

PREVIOUS SHORT TERM DISCUSSION...SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE
TO TRAVERSE ACROSS THE CWA THIS AFTERNOON...HOWEVER THE ACTIVITY
IS HIT AND MISS. SOME OF THE SHOWER ACTIVITY HAS BEEN ASSOCIATED
WITH GUSTY WINDS. EXPECT ADDITIONAL SHOWERS AND THUNDERSTORMS TO
APPROACH FROM THE SOUTHWEST THIS EVENING PER RECENT RADAR TRENDS
ACROSS CENTRAL AND SOUTHERN MONTANA.

AN ADDITIONAL SHORTWAVE WILL PUSH THROUGH THE UPPER FLOW AND MAY
SET OFF ADDITIONAL WIDELY SCATTERED SHOWERS AND THUNDERSTORMS FOR
TUESDAY ALTHOUGH THE LARGER POTENTIAL FOR SHOWERS AND
THUNDERSTORMS APPEARS TO BE ON WEDNESDAY. SREF PLUMES SHOW
INCREASING 0-6 KM EFFECTIVE SHEAR ALONG WITH MU CAPE ACROSS THE CWA
AND THIS IS SUPPORTED BY NAM BUFKIT FORECAST SOUNDINGS. AS
SUCH...A FEW STORMS MAY BE SEVERE. DUE TO PLACEMENT UNCERTAINTY
DECIDED NOT TO PUT WORDING INTO THE GRIDS RIGHT NOW. CURRENT
THINKING IS THAT LINEAR FEATURES MAY BECOME ESTABLISHED ACROSS
CENTRAL PORTIONS OF THE STATE AND PROGRESS EASTWARD. AS SUCH...DO
FEEL DAMAGING WINDS WILL BE THE PRIMARY CONCERN AS THE STORMS PUSH
EAST DURING THE EVENING AS AN UPPER LEVEL RIDGE AXIS TRANSLATES
EAST. WILL NEED TO KEEP AN EYE OUT FOR SUPER-CELLULAR MODE OF
CONVECTION EARLIER IN THE DAY AHEAD OF ANY LINEAR FEATURES THAT
ORGANIZE. THEY COULD BE ACCOMPANIED BY LARGE HAIL. HOWEVER...LARGE
SCALE SUBSIDENCE MAY MINIMIZE THAT POTENTIAL. FUTURE SHIFTS WILL
NEED TO REASSESS THE THREAT.

THE COMBINATION OF GUSTY/SHIFTING WINDS WITH STORMS ALONG WITH LOW
RELATIVE HUMIDITY READINGS AND LIGHTNING FROM THUNDERSTORMS MAY
YIELD A FIRE WEATHER THREAT ON WEDNESDAY BUT UNCERTAINTY EXISTS AT
THE MOMENT. MALIAWCO

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...

MAIN FEATURE FOR THE LONG TERM FORECAST WILL BE AN UPPER LOW
DIGGING INTO THE PACIFIC NORTHWEST. BY THURSDAY AFTERNOON...THE
LOW BECOMES NEGATIVELY TILTED WITH STRONG MID-LEVEL FLOW OVER
CENTRAL MONTANA. APPROACH OF THE LOW IS PRECEDED BY LEE TROUGHING
AND SURFACE LOW PRESSURE OVER WYOMING AND MONTANA THAT WILL ADVECT
MOISTURE INTO THE REGION. DEWPOINTS WILL BE NEAR 60 WITH CAPE
VALUES OF 1000 TO 2000 J/KG.  THE COMBINATION OF STRONG DYNAMICAL
FORCING WITH THE STORM SYSTEM...STRONG DEEP LAYER WIND SHEAR AND
MOIST-UNSTABLE AIR WILL GENERATE THUNDERSTORMS...SOME POSSIBLY
SEVERE THURSDAY AFTERNOON. A DRY LINE WILL LIKELY SET-UP ACROSS THE
CWA THURSDAY AND MOVE EASTWARD WITH THE PROGRESSING SYSTEM. EC AND
GFS MODELS DISAGREE ON PRECISE LOCATION OF DRY LINE AND CONVECTION
ON THURSDAY WITH THE GFS HAVING MOST ACTIVITY NEAR THE DAKOTAS.
THUNDERSTORMS WILL LIKELY INITIATE ALONG THE DRY LINE SOMEWHERE IN
THE CENTRAL TO EASTERN PART OF THE CWA THURSDAY AFTERNOON WITH
MOVEMENT INTO NORTH DAKOTA.

BY FRIDAY..SYSTEM AND DRY LINE ARE EAST OF THE AREA. 500MB HEIGHTS
THEN BEGIN TO BUILD OVER THE REGION. GFS IS MORE AGGRESSIVE IN THE
DEVELOPMENT OF A RIDGE OVER THE WESTERN STATES BUT BOTH MODELS
HAVE THE RIDGE AND A WARMING AND DRY TREND IN PLACE BY MONDAY. PPT
WILL BE SCARCE FRIDAY ONWARD DUE TO RIDGING.  MARTIN


&&

.AVIATION...

FLIGHT CATEGORY: VFR.

SYNOPSIS: UPPER LEVEL RIDGING WILL BUILD INTO THE REGION OVERNIGHT
LAST THROUGH THE END OF THE TERMINAL FORECAST PERIOD. A FEW
THUNDERSHOWERS REMAIN POSSIBLE ACROSS THE REGION THIS EVENING.
PROTON

&&

.FIRE WEATHER...

STILL KEEPING AN EYE ON WEDNESDAY AND THURSDAY FOR FIRE WEATHER.
WEDNESDAY IS A BIT MORE UNCERTAIN. WHILE THE HUMIDITIES DROP INTO THE
TEENS FOR THE WEST END OF THE CMR AND PETROLEUM COUNTY...THE
SOUTHEAST WINDS ARE ONLY AROUND 10 TO 15 MPH. THE STRONGER WINDS
ARE NORTH AND EAST OF THERE BUT THE HUMIDITIES WILL BE IN THE
LOWER 30S. WILL HOLD OFF ON A FIRE WEATHER WATCH FOR WEDNESDAY AT
THIS TIME. RH RECOVERY OVERNIGHT IS PRETTY POOR AS WELL WITH
READINGS IN THE 50S OVERNIGHT.

THURSDAY IS AFTER THE FRONTAL PASSAGE AND THE WINDS FROM THE
NORTHWEST WILL BE PRETTY STRONG ONCE THE FRONT PASSES THROUGH WITH
WINDS IN THE 15 TO 30 MPH RANGE. RH`S WILL BE PRETTY DRY WITH A
MORE WIDESPREAD AREA IN THE TEENS.

OVERALL MY BIGGEST CONCERN FOR FIRE WEATHER IS
LIGHTNING...POTENTIALLY DRY LIGHTNING...WITH STORMS ON WEDNESDAY
AFTERNOON/EVENING AND THEN LOW HUMIDITIES AND WINDS SHIFTING AND
INCREASING ON THURSDAY.

FRANSEN

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

WEATHER.GOV/GLASGOW





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