Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KCYS 061142 AAA
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
542 AM MDT FRI MAY 6 2016

.UPDATE...FOR THE EARLY MORNING AVIATION FORECAST PACKAGE UPDATE.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 401 AM MDT FRI MAY 6 2016

AN EXTREMELY ACTIVE PERIOD OF WEATHER OVER THE NEXT FEW DAYS WITH AT
LEAST SOME POTENTIAL FOR SEVERE THUNDERSTORMS...FLASH FLOODING...AND
ACCUMULATING MOUNTAIN SNOW. MORNING WATER VAPOR AND OBJECTIVE UPPER-
AIR ANALYSIS REVEAL AN IMPRESSIVE OMEGA BLOCK ENCOMPASSING VIRTUALLY
ALL OF THE LOWER 48. HIGH-AMPLITUDE RIDGING OVER THE GREAT PLAINS IS
EXPECTED TO BREAK DOWN OVER THE NEXT 12 HOURS...BUT EXPECT VERY SLOW
PROGRESSION OF THE SOUTHWESTERN US LOW GIVEN THE CURRENT LARGE SCALE
BLOCKING PATTERN IN PLACE.

SOUTHWEST FLOW ALOFT IS ALREADY INCREASING OVER THE CWA THIS AM WITH
DEEP MOISTURE STREAMING NORTHWARD. WE WILL NOT SEE AS MUCH SUN AS WE
HAVE OVER THE LAST FEW DAYS...BUT EXPECT ANOTHER MILD AFTERNOON WITH
MODELS STILL SHOWING H7 TEMPS BETWEEN +8 AND +10 DEG C. IT WILL ALSO
BE A WARM START TO THE DAY WITH CHEYENNE SITTING AT 53 DEGREES AS OF
3 AM MDT. WEAK SURFACE CYCLOGENESIS WILL OCCUR OVER NORTHEASTERN
CO TODAY...RESULTING IN LOW-LEVEL UPSLOPE ALONG AND EAST OF THE
LARAMIE RANGE HEADING INTO THIS AFTERNOON. LOW-LEVEL MOISTURE IS
EXPECTED TO INCREASE WITH DEW POINTS IN THE 40S TO NEAR 50. WARM
TEMPERATURES AT THE SURFACE WILL PROMOTE STEEP LAPSE
RATES...POSSIBLY YIELDING CAPES AROUND 500-1000 J/KG AREAWIDE.
FORECAST SOUNDINGS LOOK FAVORABLE FOR STRONG TO LOCALLY SEVERE
CONVECTION...SO ADDED MENTION OF SMALL HAIL AND GUSTY WINDS FOR
ALL ZONES THIS AFTERNOON. THE 06Z DY1 CONVECTIVE OUTLOOK FROM SPC
HAS MUCH OF THE AREA IN A MARGINAL RISK. A PIECE OF MID-LEVEL VORT
ENERGY IS PROGGED TO ROTATE ACROSS SOUTHEAST WYO LATE
TONIGHT...BETWEEN 00Z AND 12Z SAT. BELIEVE THIS WILL INTERACT WITH
A PRONOUNCED FRONTAL BOUNDARY AND DEEP UPSLOPE FLOW TO PRODUCE AN
AREA OF MODERATE TO HEAVY PRECIPITATION OVER OUR NORTHERN
ZONES...SO WENT AHEAD AND INTRODUCED CATEGORICAL POPS PER
COORDINATION WITH UNR.

BIG CHALLENGES WITH THE FORECAST FOR SATURDAY. MODELS SHOW THE UPPER
LOW CENTERED OVER THE FOUR CORNERS WITH ONE OR MORE SIGNIFICANT VORT
LOBES AFFECTING THE CWA...THE STRONGER OF WHICH APPEARS TO ARRIVE IN
THE LATE AFTERNOON/EVENING. STRONG DYNAMIC SUPPORT IS LIKELY THROUGH
THE DAY WITH CYCLOGENESIS OVER NORTHEAST CO REINFORCING UPSLOPE FLOW
AND UPPER-LEVEL DIVERGENCE IN THE LEFT EXIT REGION OF A 100-110 KNOT
H25 JET OVER SOUTHEAST CO. SEVERE THUNDERSTORMS ARE STARTING TO LOOK
LIKE MORE OF A THREAT...MAINLY IN THE CYS-TOR-SNY TRIANGLE AND AREAS
TO THE SOUTH AND EAST. WOULD LIKE TO SEE THE POSITION OF THE SURFACE
LOW FARTHER NORTHWEST FOR A BIG OUTBREAK...BUT NONETHELESS THIS DOES
SUPPORT MOIST EASTERLY SFC FLOW VEERING TO THE SOUTHEAST AT H7 WHICH
YIELDS SHEAR PROFILES FAVORABLE FOR SUPERCELLS. BOTH THE GFS AND NAM
SHOW 1500-2500 J/KG OF SBCAPE AND EXCELLENT 0-1 KM EHI GIVEN LOW-LVL
SHEAR IN PLACE. SLIGHT RISK FROM SPC NOW INCLUDES I80 BETWEEN SIDNEY
AND CHEYENNE...SO DECIDED TO ADD MENTION OF SEVERE. CIPS ANALOGS ARE
CONSISTENT WITH SEVERAL NORTHEAST COLORADO TORNADO EVENTS...SO WOULD
NOT BE SURPRISED TO SEE AN ISOLATED TORNADO OR TWO NEAR THE COLORADO
BORDER ON SATURDAY.

IN ADDITION TO THE RISK FOR SEVERE THUNDERSTORMS...A MORE WIDESPREAD
THREAT FOR VERY HEAVY RAIN IS EXPECTED. DEEP MOISTURE AND IMPRESSIVE
LARGE SCALE DYNAMICS WILL BE IN PLACE THROUGH THE NIGHT AS THE UPPER
LOW WILL BE SLOW MOVING DUE TO A REX BLOCK. ABSOLUTELY NO DOUBT THAT
THUNDERSTORMS ON SATURDAY/SATURDAY NIGHT WILL BE VERY EFFICIENT RAIN
PRODUCERS WITH PWATS OF 0.5 TO 1.0 INCH BEING WELL ABOVE CLIMO. SOME
CONCERN FOR TRAINING CONVECTION AS WELL. THE PRIMARY ISSUE HERE WILL
LIKELY BE OVER THE HIGHER TERRAIN WITH AN ENHANCED LIKELIHOOD FOR AN
ACCELERATED SNOWMELT AND FLASH FLOODING OF CREEKS/STREAMS. GAVE SOME
CONSIDERATION TO A FLASH FLOOD WATCH...BUT WE DECIDED TO LET THE DAY
SHIFT TAKE ANOTHER LOOK AND SEE IF THEY CAN NARROW DOWN THE SPECIFIC
THREAT AREAS. WPC HAS MUCH OF OUR CWA IN A SLIGHT RISK FOR EXCESSIVE
RAINFALL ON SATURDAY...SO FULLY EXPECT THAT FLOOD AND/OR FLASH FLOOD
WATCHES WILL BE NECESSARY SOON. BY LATE SATURDAY NIGHT...WBZ HEIGHTS
FINALLY DROP BELOW 10K FEET WHICH WOULD SUGGEST MOUNTAIN SNOW. COULD
SEE ADVISORY-LEVEL AMOUNTS IF THE CHANGEOVER OCCURS SOON ENOUGH OVER
THE SNOWY AND SIERRA MADRE RANGES.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 401 AM MDT FRI MAY 6 2016

WET PATTERN CONTINUES INTO SUNDAY AS THE UPPER LOW ESSENTIALLY
STALLS ACROSS SOUTHEAST WYOMING WITH HIGH CHANCE TO LIKELY POPS A
FAIRLY GOOD BET ACROSS THE ENTIRE FORECAST AREA. CONCERNS FOR
FLOOD POTENTIAL WILL CONTINUE INTO SUNDAY GIVEN COVERAGE OF RAIN
BUT COOLER TEMPERATURES SHOULD MEAN MORE SNOW IN THE HIGHER
ELEVATIONS VERSUS RAIN BY LATE IN THE WEEKEND. THE AIRMASS WILL
BE A BIT MORE STABILIZED ON SUNDAY DUE TO COOLER BOUNDARY
LAYER CONDITIONS...HOWEVER WE STILL EXPECT TO SEE THE POTENTIAL
FOR ISOLATED THUNDERSTORMS IN THE AFTERNOON TO EARLY EVENING
HOURS. THE UPPER LOW FINALLY KICKS OUT TO THE NORTHEAST LATE
MONDAY WITH A DOWNWARD TREND IN POPS EXPECTED ACROSS THE SOUTHERN
ZONES TUESDAY WITH CHANCE POPS FOR SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE NORTHERN ZONES AHEAD OF THE NEXT
APPROACHING UPPER TROUGH MOVING DOWN FROM MONTANA. THAT TROUGH
MOVES EAST BY THURSDAY WITH SLIGHT CHANCE POPS EXPECTED GOING INTO
LATE WEEK. OVERALL NEXT WEEK LOOKS TO BE COOLER THAN WHAT WE HAVE
SEEN THE LATTER PART OF THIS WEEK WITH DAILY HIGH TEMPS GENERALLY
IN THE 40S-50S WEST AND 60S EAST. ELEVATIONS ABOVE 9500 FT LOOK
TO SEE HIGHS IN THE MID 30S TO AROUND 40 THROUGH THE WEEK...COOL
ENOUGH TO SLOW THE SNOWMELT PROCESS A BIT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 542 AM MDT FRI MAY 6 2016

FOLLOWED TREND AS DEPICTED BY HRRR THIS PACKAGE IN BRINGING
SHOWERS AND ISOLATED THUNDERSTORMS UP INTO SE WYOMING MID TO LATE
AFTERNOON THEN INTO THE NEBRASKA PANHANDLE BY EARLY EVENING.
CEILINGS AND VISIBILITIES PREVAILING VFR THROUGH LATE AFTERNOON
INTO THE EVENING HOURS WITH SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS PASSING ACROSS THE REGION. LOWERED CEILINGS FOR
SCOTTSBLUFF, CHEYENNE, LARAMIE AND RAWLINS DOWN TO MVFR AFTER 06Z
WHERE GREATER COVERAGE OF SHOWERS WILL BE AS DEEPER MOISTURE MOVES
UP FROM THE SOUTH.

&&

.FIRE WEATHER...
ISSUED AT 401 AM MDT FRI MAY 6 2016

COOLER AND WETTER PATTERN STILL PROJECTED TO SET UP ACROSS SE
WYOMING AND THE WESTERN NEBRASKA PANHANDLE THROUGH THE WEEKEND.
PATTERN BECOMES A BIT LESS ACTIVE FOR SHOWERS AND THUNDERSTORMS
BY MID WEEK WITH PROJECTED CONDITIONS EXPECTED TO REMAIN WELL
ABOVE ANY CRITICAL THRESHOLDS FOR FIRE WEATHER CONCERNS IN THE
FORSEEABLE FUTURE.

&&

.HYDROLOGY...
ISSUED AT 401 AM MDT FRI MAY 6 2016

WARM TEMPERATURES WILL CONTINUE TODAY WITH AFTERNOON HIGHS LIKELY IN
THE 50S IN THE HIGH ELEVATIONS OF THE SNOWY/SIERRA MADRE RANGES. MTN
CREEKS AND STREAMS WILL CONTINUE TO SEE NOTABLE RISES IN THE NEXT 24
TO 48 HOURS. WIDESPREAD THUNDERSTORMS COULD PRODUCE HEAVY RAIN TODAY
AND SATURDAY. RAIN ON SNOW COULD YIELD ACCELERATED SNOWMELT AND LEAD
TO FLASH FLOODING...ESPECIALLY OF MOUNTAIN CREEKS/STREAMS. THERE MAY
ALSO BE A THREAT FOR LOCALIZED FLASH FLOODING OVER THE PLAINS. FLASH
FLOOD WATCHES MAY BECOME NECESSARY SOON.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...JG
AVIATION...JG
FIRE WEATHER...JG
HYDROLOGY...CLH


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.