000
FXUS65 KGGW 220218
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
818 PM MDT TUE MAY 21 2013

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

MODEST UPDATE THIS EVENING. REDUCED OVERNIGHT TEMPERATURES SOME AS
THERE IS SOME CLEARING IN WESTERN PARTS OF THE CWA AND DEWPOINTS
ARE WELL BELOW GUIDANCE VALUES. HRRR AND NAM HINT AT SOME POSSIBLE
LIGHT SHOWERS OVER SOUTHERN PARTS OF THE CWA TONIGHT IN RESPONSE
TO A SUBTLE IMPROVEMENT IN THE UPPER FLOW...SO SPREAD THE SLIGHT
CHANCE FOR A SHOWERS IN THE FORECAST WESTWARD TO PHILLIPS COUNTY.

NEXT SEVERAL DAYS LOOK TO BE SOMEWHAT WINDY AS A STRONG SURFACE
LOW DEVELOPS OVER WESTERN WYOMING AND MONTANA AHEAD OF THE NEXT
LONG WAVE SYSTEM...AND THE LAKE WIND ADVISORY MIGHT BE NEEDED
THROUGH FRIDAY. MARTIN

PREVIOUS DISCUSSION...
AN UPPER LEVEL LOW OVER EASTERN SOUTH DAKOTA WILL
CONTINUE TO DRIVE WRAPAROUND LIGHT SHOWER ACTIVITY OVER THE
SOUTHEAST THIS EVENING. SHOWER ACTIVITY WILL QUICKLY TAPER OFF
AFTER MIDNIGHT AS THE UPPER LOW PUSHES TO THE EAST.

DRY AND WARM CONDITIONS WILL RULE ON WEDNESDAY AS UPPER RIDGING
DOMINATES AHEAD OF AN APPROACHING UPPER TROUGH OVER THE PACIFIC
NORTHWEST. GUSTY SOUTHEAST WINDS WILL ALSO PICK UP DURING THE LATE
MORNING IN RESPONSE TO THE APPROACHING LOW...NECESSITATING A LAKE
WIND ADVISORY THAT WILL LAST INTO LATE THURSDAY EVENING.

SOUTHERLY FLOW ALOFT ASSOCIATED WITH THE APPROACHING UPPER LOW
LOOKS TO BUILD INTO THE WESTERN ZONES BY WEDNESDAY EVENING.
DISTURBANCES IN THIS FLOW WILL CREATE DECENT CHANCES FOR SHOWERS
AND THUNDERSTORMS ACROSS THE WEST INTO THURSDAY. GILCHRIST


.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
THE UPPER LEVEL RIDGE GETS PUSHED ASIDE THURSDAY NIGHT AND FRIDAY
BY A LOBE OFF THE STRONG PAC-NW CLOSED LOW SWINGING NORTH THROUGH
MONTANA. WEAK INSTABILITY DEVELOPS TO THE SOUTHWEST LATE THURSDAY
SO THE DISTURBANCE COULD GENERATE SCATTERED RAIN SHOWERS AND
ISOLATED THUNDER MAINLY IN THE WESTERN ZONES. A MORE DISTINCT COLD
FRONT WILL PUSH THROUGH THE AREA ON FRIDAY...BUT AGAIN...THE BEST
INSTABILITY AND MOISTURE REMAIN OUTSIDE NORTHEAST MONTANA...
ACCORDING TO THE GFS. THE TIMING IS DIFFERENT IN THE EC...WHICH COULD
BRING THE FRONT INTO THE AREA FRIDAY AFTERNOON WITH INSTABILITY.
WITH MODEL DIFFERENCES ON FRIDAY...WILL LEAVE POPS AS IS. MODEL
DIFFERENCES CONTINUE INTO SATURDAY. THERE COULD BE SHOWERS AND
THUNDER OR NOT...DEPENDING ON THE MODEL. SO AGAIN WILL LEAVE
ALONG. THERE IS AT LEAST THE POTENTIAL WITH THE GFS MODEL TO MATCH
UP A TEMPERATURE BOUNDARY WITH SOME VERY UNSTABLE CONDITIONS...
WHICH COULD LEAD TO SOME ENERGETIC THUNDERSTORMS. SUNDAY LOOKS
LIKE THE BEST DAY FOR TIMING AND LOCATION TO BRING ABOUT POSSIBLY
VERY ENERGETIC STORMS. THE GRIDS HANDLE THIS UNCERTAINTY WELL...SO
FEW CHANGE PAST DAY FOUR. SCT

PREVIOUS DISCUSSION... THE EXTENDED PERIOD BEGINS THURSDAY NIGHT
WITH A CLOSED UPPER TROUGH ACROSS THE WEST AND AN UPPER LEVEL
RIDGE ACROSS THE SOUTHERN U.S. THAT EXTENDS THROUGH THE PLAINS.
THIS PLACES NORTHEAST MONTANA IN DIFFLUENT SOUTHWEST FLOW ALOFT.
THE 00Z MODEL SUITE IS POINTING TO A ROBUST SHORTWAVE PUSHING
THROUGH THE FLOW WHICH COULD LEAD TO ENHANCED DYNAMIC LIFT ACROSS
PARTS OF THE CWA. THE 850MB LEVEL EASTERLY/SOUTHEASTERLY WINDS
WILL HELP TO PUMP IN LOW LEVEL MOISTURE...AND ALSO SUGGEST THE
PRESENCE OF A LOW LEVEL JET WHICH COULD HELP TO FORCE CONVECTION
IF THE OTHER DYNAMIC INGREDIENTS DISCUSSED COME TOGETHER
COINCIDENT LY. DECENT EQUIVALENT POTENTIAL TEMPERATURE RIDGE LOOKS
TO BE IN PLACE ACROSS THE CWA BY FRIDAY AFTERNOON WITH WARMING
TEMPERATURES OUT AHEAD OF THE TROUGH. THE MID LEVELS ALSO LOOK
PRETTY DRY. THIS LEADS TO THE CONCERN THAT SOME STORMS THAT
DEVELOP MAY PRODUCE HAIL. THE 00Z ECMWF FORECAST SOUNDINGS SHOW LI
BETWEEN -1 AND 1 ACROSS THE CWA AND TOTAL TOTALS IN THE UPPER 40S
AND NOT MUCH CAPE. NOTICE A NICE VEERING PROFILE IN THE ECMWF
FORECAST SOUNDINGS WITH ABOUT 40 KTS OF 0-6 KM SPEED SHEAR. THE
GFS SHOWS ACTUALLY HIGHER LIFTED INDEX VALUES AND IS LESS
SUGGESTIVE OF STRONG CONVECTION IN SHORT...THE INGREDIENTS ARE
THERE FOR GOOD THUNDERSTORM DEVELOPMENT BUT SOME PARAMETERS APPEAR
ONLY MARGINAL AND SO CONFIDENCE ON STRONG STORMS IS NOT YET THERE.
WILL NEED TO LOOK AT FUTURE MODEL RUNS FOR CONSISTENCY. TIMING OF
THE SHORTWAVE AS IT INTERSECTS THE THETA-E RIDGE WILL ALSO BE
KEY...RIGHT NOW IT APPEARS THE NORTHERN ZONES AND SOUTHERN
SASKATCHEWAN MAY BE IN THE BEST LOCATION FOR FRIDAY AFTERNOON FOR
CONVECTION INITIATION IF FOLLOWING THE EC GUIDANCE. ANY CONVECTION
SHOULD SLOWLY DWINDLE FRIDAY NIGHT WITH THE LOSS OF DAYTIME
HEATING.

ON SATURDAY...UPPER FLOW PATTERN MAINTAINS SOUTHWEST FLOW ALOFT
OVER THE CWA WITH RIDGE AXIS RUNNING FROM TEXAS...NORTHWESTWARD
THROUGH THE PLAINS AND INTO NE MT. THIS SHOULD ACTUALLY LEAD TO
WARMER TEMPERATURES WHICH COULD LEND TO ENHANCING THE POTENTIAL
FOR CONVECTION INITIATION. NICE UPPER LEVEL DIFFLUENCE IS NOTED
AND SOME OF THE FORECAST SOUNDINGS ARE CERTAINLY INDICATIVE OF
CONVECTIVE POTENTIAL. THERE IS ALSO SOME SUBTLE EMBEDDED SHORTWAVE
ENERGY THAT PUSHES THROUGH SHORTWAVE FLOW ALOFT...BUT NOTHING AS
IMPRESSIVE AS THE WAVE ON FRIDAY.

SUNDAY INTO SUNDAY NIGHT PRESENTLY LOOKS TO BE THE BEST POTENTIAL
FOR THUNDERSTORMS TO DEVELOP WHICH COULD BECOME STRONG IN NATURE.
THERE IS MUCH BETTER AGREEMENT IN BOTH THE ECMWF AND GFS WITH BOTH
FORECAST SOUNDINGS SHOWING LIFTED INDEX VALUES BETWEEN -5 AND -8
ACROSS THE CWA. THE GFS BUFKIT SOUNDING SHOWS AROUND 1500 J/KG OF
CAPE AND TOTAL TOTALS APPROACHING 60. THOUGH A NICE VEERING WIND
PROFILE EXISTS IN BOTH ECMWF/GFS SOUNDINGS... THOUGH WOULD LIKE
TO SEE MORE SPEED SHEAR IN THE SOUNDINGS. SHOULD ALSO POINT OUT
THAT FORECAST SOUNDINGS FROM BOTH MODELS ARE SHOWING PWATS OF OVER
AN INCH. WITH AGAIN DRY AIR PRESENT IN THE MID LEVELS...WOULD BE
CONCERNED ABOUT HAIL FORMATION WITH ANY STORMS. THERE IS AGAIN A
LOW LEVEL 850MB EASTERLY JET THAT FORMS...WHICH SHOULD HELP TO
PUMP IN LOW LEVEL MOISTURE. NICE THETA-E RIDGE AXIS OVER THE CWA
ALONG WITH A COUPLE OF SHORTWAVES THAT PASS OFF TO THE WEST COULD
ALSO HELP PROVIDE DECENT LIFT IF THE TIMING IS RIGHT...AND THAT
WILL BE THE KEY FOR DETERMINING THE OVERALL EXTENT OF THE
THUNDERSTORM POTENTIAL. OF ALL OF THE DAYS IN THE EXTENDED
PERIOD...THIS LOOKS TO BE THE ONE WITH THE BEST MODEL AGREEMENT
AND THE BEST IN TERMS OF VARIOUS INGREDIENTS COMING TOGETHER BOTH
DYNAMICALLY AND THERMODYNAMICALLY THAT ARE COINCIDENT WITH EACH
OTHER. WILL OF COURSE NEED TO WATCH FOR CONTINUITY IN THE MODEL
SOLUTIONS TO DETERMINE IF THIS CONTINUES. WILL ALSO NEED TO HONE
IN ON MESOSCALE DETAILS WHICH ARE DIFFICULT TO DETERMINE THIS FAR
IN ADVANCE. WHERE THESE INGREDIENTS COME TOGETHER...THE PRECISE
TIMING OF THE SHORTWAVE FEATURES...AND HOW EVERYTHING INTERACTS
WITH MESOSCALE PROCESSES WILL DETERMINE THE PRECISE EXTENT OF
CONVECTIVE POTENTIAL.

MONDAY AND BEYOND...NE MT IS EXPECTED TO REMAIN IN SOUTHWEST FLOW
ALOFT WITH THE ECMWF GUIDANCE SUGGESTING PERHAPS THE UPPER
PATTERN COULD BECOME MORE ZONAL LATE NEXT WEEK. THE GFS ON THE
OTHER HAND KEEPS THE OVERALL PATTERN ALOFT FROM THE SOUTHWEST. THIS
OVERALL PATTERN WOULD BE CONSIDERED FAVORABLE FOR A CONTINUED
POTENTIAL FOR CONVECTIVE SHOWERS AND THUNDERSTORMS TO DEVELOP
DEPENDING ON TIMING/TRACK OF SHORTWAVE FEATURES IN THE FLOW. MALIAWCO.

&&

.AVIATION...
PREVAILING VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.
CANNOT RULE OUT SOME LOW END VFR/MARGINAL MVFR CEILINGS FOR A TIME
AT KSDY AND KGDV THROUGH TONIGHT. LOOK FOR PERSISTENT 10 TO 20 KT
EASTERLY WINDS THROUGH THE OVERNIGHT...INCREASING TO 15 TO 25 KT
ON WEDNESDAY. MALIAWCO

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY FROM 10 AM WEDNESDAY TO MIDNIGHT MDT THURSDAY
NIGHT FOR FORT PECK LAKE FOR CENTRAL AND SOUTHEAST PHILLIPS...
CENTRAL AND SOUTHERN VALLEY...GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW