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000
FXUS65 KBOU 180154
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
754 PM MDT FRI MAY 17 2013

.UPDATE...THUNDERSTORM THREAT HAS PRETTY MUCH SHIFTED NORTHEAST
OF THE FORECAST AREA WITH DRY AND CAPPED AIRMASS SPREADING ACROSS
THE NORTHEAST PLAINS. THE ONLY WAY THE FAR NORTHEAST CORNER COULD
SEE A STORM IS OUTFLOW INTERACTION FROM NEBRASKA CONVECTION...BUT
DEEP SOUTHERLY FLOW IN PLACE SHOULD KEEP BOUNDARIES FROM MAKING
MUCH SOUTHWARD PROGRESS.

LOW LEVEL DEWPOINTS WILL CONTINUE TO INCREASE OVER THE NORTHEAST
PLAINS OVERNIGHT IN SOUTH/SOUTHEASTERLY FLOW...SO HAVE ADDED SOME
STRATUS AND FOG OVER THE FAR EASTERN PLAINS OVERNIGHT. NO CHANGES
TO REST OF FORECAST.

SEVERE THREAT REMAINS EAST OF THE DRYLINE REMAINS TOMORROW
AFTERNOON...ALTHOUGH FLY IN THE OINTMENT COULD BE HIGH CLOUDINESS
WHICH WOULD REDUCE COVERAGE AND/OR DELAY INITIATION. WILL
CONTINUE TO MONITOR.

&&

.AVIATION...SURFACE WIND FORECAST DIFFICULT OVER THE NEXT COUPLE
HOURS WITH DENVER CONVERGENCE ZONE JUST WEST OF THE AIRPORT. IT
SEEMS TO HAVE SLOWED IN THE LAST 30 MINUTES SO WEST/NORTHWEST WIND
SHIFT MAY NOT OCCUR THIS EVENING. ANY CONVECTION SATURDAY
AFTERNOON WILL BE HIGH BASED...BUT MAIN CONCERN WILL BE POTENTIAL
WIND GUSTS TO 30-40 KTS FROM THE WEST/NORTHWEST DUE TO OUTFLOW
FROM MOUNTAIN SHOWERS.

&&

.HYDROLOGY...NO CONCERNS.

&&

.PREV DISCUSSION... /ISSUED 317 PM MDT FRI MAY 17 2013/

SHORT TERM...IN FOR SOME IMPORTANT CHANGES TO OUR WEATHER DURING
THE NEXT 24-36 HOURS. ABNORMALLY STRONG UPPER TROUGH FOR THIS TIME
OF YEAR WAS MAKING SLOW EASTWARD PROGRESS ACROSS THE GREAT BASIN
THIS AFTERNOON. IT IS THIS TROUGH AND THE STRONG FLOW ROUNDING
THE BOTTOM OF THIS TROUGH TOGETHER WITH INCREASING LOW TO MID-
LEVEL SHEAR AND STEEP LAPSE RATES THAT COULD POTENTIALLY GENERATE
SEVERE T-STORMS ON THE NORTHEAST PLAINS OF COLORADO MID TO LATE
SATURDAY AFTERNOON. LAST NIGHT`S MODELS SHOWED A SFC-850 LOW
SPINNING UP IN NORTHEAST COLORADO BY SATURDAY AFTERNOON IN
PROXIMITY OF A TRIPLE POINT. LATEST NAM RUN NOW SHOWS THIS LOW A
BIT FARTHER EAST...WHILE THE GFS HAS IT STRADDLING THE COLO/KANS
LINE AS OF 00Z/SUN. A DRY LINE EXTENDS SOUTH OUT OF THE LOW WITH A
MOISTURE RICH SOUTHEASTERLY BNDRY LAYER FLOW TO ITS EAST. MODELS
BY LATE AFTERNOON INDICATE FAVORABLE HELICITIES AND SFC BASED CAPE
VALUES WELL OVER 2000 JOULES/KG EAST OF THE DRY LINE. WHERE THIS
DRY LINE SETS UP WILL ALL DEPEND WHERE STORMS WILL FIRE AND THEIR
MAGNITUDE. SHOULD THE SFC-850 LOW AND ITS DRY LINE HAPPEN TO FORM
CLOSER TO THE FRONT RANGE AS THE EARLIER NAM SUGGESTED...COULD SEE
SCATTERED T-STORMS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND
POSSIBLY ISOLATED TORNADOES ACROSS THE NORTHEAST CORNER OF THE
STATE SOMETIME AFTER 20Z TOMORROW. AS IT STANDS NOW...MAY SEE THE
BULK OF THIS STRONG CONVECTION RIGHT ALONG THE COLORADO/KANSAS/
NEBRASKA BORDER. SPC INDICATES A MODERATE RISK OF SEVERE JUST EAST
OF THE STATE LINE TOMORROW. MUST WATCH HOW THIS PATTERN DEVELOPS
AS THIS MODERATE RISK AREA COULD SLIP BACK INTO NORTHEAST
COLORADO.

FOR THE REMAINDER OF TODAY...A DRY LINE NOW LYING ACROSS LOGAN AND
EASTERN WASHINGTON COUNTIES COULD SERVE AS A  FOCUS FOR ISOLATED
T-STORM FORMATION IN THE NEXT 1 TO 2 HOURS. CAPES EAST OF TODAY/S
DRY LINE NOT AS HIGH AS THOSE PROGGED FOR TOMORROW AT THIS
TIME...BUT SHEAR AND INSTABILITY OUT THERE COULD GENERATE A FEW
SINGLE CELLS CAPABLE OF HAIL TO AROUND 1 INCH IN DIAMETER AND WIND
GUSTS TO 60 MPH. PHILLIPS AND SEDGWICK COUNTIES ARE PROBABLY IN
THE BEST POSITION TO SEE THESE STORMS THIS EVENING. STORMS SHOULD
MOVE OUT OF THE STATE BY MID TO LATE EVENING WITH DRY
SOUTHWESTERLY FLOW SPREADING OFF THE FRONT RANGE IN RESPONSE TO
INCREASING SOUTHWESTERLY FLOW ALOFT IN ADVANCE OF THE BIG TROUGH
TO OUR WEST.


LONG TERM...MODELS SHOW UPPER TROUGH MOVING INTO CENTRAL COLORADO
SATURDAY EVENING...SPREADING MOISTURE ACROSS THE REGION. INCREASING
ASCENT TO HELP INCREASE THE CHANCES FOR SHOWERS AND THUNDERSTORMS
OVER THE CFWA...THOUGH WESTERLY DOWNSLOPE ALONG THE URBAN CORRIDOR
MAY LIMIT THE ACTIVITY. OF CONCERN...THOUGH...IS THE POTENTIAL FOR
SEVERE THUNDERSTORMS OVER THE NORTHEAST CORNER THROUGH AROUND 03Z
WHERE MODELS SHOW LOW LEVEL CONVERGENCE AND POOLING OF MOISTURE
ALONG WITH GOOD SHEAR DUE TO EASTERLIES AT THE SURFACE AND SOUTHWEST
TO WEST WINDS ALOFT. THOUGH BEST CAPES PROGGED TO OCCUR DURING THE
AFTERNOON...MODELS STILL SHOW CAPES AROUND 1000-1500 JOULES/KG.
THREAT DOES EXIST FOR LARGE HAIL AND STRONG WIND...WITH PERHAPS A
TORNADO. THREAT DIMINISHES AFTER 03Z AS CONVERGENCE LINE SHIFTS
EAST AND SHEAR WEAKENS. FOR THE OVERNIGHT SATURDAY...UPPER TROUGH
TO BE OVER THE STATE ALLOWING FOR COOLER AIR AND MOISTURE TO
SPREAD OVER THE AREA. WEAK ASCENT WILL COMBINE WITH INFLUX OF
MOISTURE TO PRODUCE AT LEAST A CHANCE OF SHOWERS. AIRMASS APPEARS
ONLY SLIGHT UNSTABLE BASED ON LAPSE RATES AROUND 5-6C/KM. PERHAPS
THERE MAY BE A THREAT OF THUNDER BUT FOR NOW WILL NOT MENTION IN
THE GRIDS. TEMPERATURES COULD COOL SUFFICIENTLY FOR SOME SNOW OVER
THE HIGHER RIDGES...NOT EXPECTING MUCH IN THE WAY OF ACCUMULATION AT
THIS TIME. MODELS SHOW TROUGH REMAINING OVER THE AREA SUNDAY AND
MONDAY WITH COOL AND UNSETTLED WEATHER PATTERN FOR THE CFWA. THIS
WILL WILL RESULT IN PERIODS OF SHOWERS ALONG WITH THE POSSIBILITY
OF THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS. FORCING
WITH THE TROUGH DOES NOT APPEAR ALL THAT STRONG...SO NOT EXPECTING
HEAVY RAINFALL. MONDAY STILL LOOKING LIKE THE COOLER DAY OF THE
TWO...WITH TEMPERATURES ACROSS THE PLAINS IN THE LOWER AND MID
60S. FOR TUESDAY...MODELS STILL SHOWING THE TROUGH MOVING INTO THE
CENTRAL PLAINS WITH THE FLOW ALOFT BECOMING NORTHWEST. DRIER AND
SLIGHTLY WARMER AIR WILL BEGIN TO SPREAD ACROSS THE STATE. STILL
ENOUGH MOISTURE ACROSS THE MOUNTAINS FOR SOME SHOWERS AND
THUNDERSTORMS...MAINLY DURING THE AFTERNOON. A FEW STORMS ALSO
POSSIBLE OVER THE FAR EASTERN PLAINS. TEMPERATURES OVER NORTHEAST
COLORADO TO WARM TO NEAR 70 DEGREES.

FOR THE LATER PERIODS WEDNESDAY THROUGH FRIDAY...UPPER RIDGE
EXPECTED TO BE OVER THE STATE WEDNESDAY. THIS WILL RESULT IN DRIER
AND WARMER CONDITIONS WITH ONLY A SLIGHT CHANCE OF AFTERNOON
STORMS OVER THE HIGH COUNTRY. FOR THURSDAY AND FRIDAY...MODELS
SHOW UPPER TROUGH MOVING INTO THE NORTHERN GREAT BASIN WITH THE
FLOW ALOFT BECOMING SOUTHWEST. WEAK EASTERLY FLOW AND SOME
INCREASE IN LOW LEVEL MOISTURE MAY BE SUFFICIENT FOR A SLIGHT
CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS...MAINLY FOOTHILLS
AND PLAINS. TEMPERATURES LOOK TO WARM TO NEAR 80 DEGREES ACROSS
NORTHEAST COLORADO.

AVIATION...VFR CONDITIONS EXPECTED IN THE DENVER AREA THROUGH
21Z SATURDAY AFTERNOON. AFTER 21Z...THE DENVER AREA COULD SEE
ISOLATED T-STORMS CAPABLE OF WIND GUSTS TO 35 KTS AND BRIEF LIGHT
TO MODERATE RAINFALL. WHILE VFR CONDITIONS WILL PREVAIL...COULD
SEE A BRIEF REDUCTION IN VISIBILITY WITH PASSING LATE DAY SHOWERS.
AS FOR WINDS...EXPECT EAST-SOUTHEAST WINDS OF 8-15KTS AT THIS
TIME...ARE EXPECTED TO BECOME NORTH-NORTHWEST AT 7-10KTS FOR A
SHORT TIME EARLY THIS EVENING...THEN SOUTH-SOUTHWEST 8-14KTS
OVERNIGHT. ON SATURDAY...LOOK FOR WINDS IN THE METRO AREA TO
GRADUALLY BECOME WEST-NORTHWEST 8-13KTS BY LATE SATURDAY MORNING.

HYDROLOGY...NO CONCERNS AT THIS TIME.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARJENBRUCH
LONG TERM....D-L
AVIATION...BARJENBRUCH