Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 221407
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1007 AM EDT TUE JUL 22 2014

.SYNOPSIS...
HIGH PRESSURE OFF THE DELMARVA COAST WILL REMAIN ALONG THE EASTERN
SEABOARD TODAY. A COLD FRONT OVER MINNESOTA IS EXPECTED TO TRACK
INTO THE MID ATLANTIC STATES EARLY THURSDAY. HIGH PRESSURE IS
EXPECTED TO RETURN TO THE REGION TO END THE WORKWEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
HIGH PRESSURE LATE THIS MORNING EXTENDS FROM THE OFFSHORE WATERS
ACROSS THE FORECAST AREA AND INTO WEST VIRGINIA. MOSTLY STRATUS
CLOUDS WITH A FEW BREAKS EAST OF THE BLUE RIDGE...WHILE MOST AREAS
WEST OF THE BLUE RIDGE HAVE BECOME CLEAR TO PARTLY CLOUDY. 12Z
SOUNDINGS INDICATE WARM NOSE AROUND 600 MB. THIS SHOULD LIMIT
COVERAGE OF ANY SHOWER OR ISOLATED TSTM ACTIVITY.
HOWEVER...SURFACE BASED INSTABILITY IS EXPECTED TO EXCEED 1000
J/KG OVER AREAS WHERE LOW CLOUDS BREAK UP. WILL CONTINUE TO CARRY
POSSIBILITY OF ISOLATED OR SCATTERED SHOWERS...AND ISOLATED TSTMS
FOR MOST AREAS EXCEPT THE EASTERN HALF OF MD. GIVEN WEAK WIND
FIELDS...ANY STORMS SHOULD BE SHORT-LIVED. HIGH TEMPS GENERALLY IN
THE M80S ACROSS THE FORECAST AREA.

&&

.SHORT TERM / WEDNESDAY THROUGH 6 AM WEDNESDAY/...
NOT MUCH CHG TNGT OVR THE PAST FEW NGTS - LO LV MOISTURE WL CAUSE
SKIES TO BE PC/MC. LO TEMPS GNRLY IN THE U60S...LM70S IN THE CITIES.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
WEDNESDAY THROUGH THURSDAY NIGHT/
TRENDS TOWARD A SLIGHTLY STRONGER UPPER RIDGE OVER THE ROCKIES/CNTRL
PLAINS DURING THE MIDDLE OF THIS WEEK IS HAVING AN EFFECT ON THE
REST OF THE CONUS. THE RESULT IN TERMS OF THE UPPER TROUGH DIGGING
DOWN ACROSS THE GREAT LAKES WILL BE A SLIGHTLY WARMER DAY ON WED -
AS WELL AS A QUICKER ARRIVAL OF THE UPPER WAVE. TRENDS IN MED RANGE
GUIDANCE SINCE THE DAY BEFORE HAVE BEEN FOR THE TROUGH AXIS TO MORE
QUICKLY DIG DOWN ACROSS THE OHIO VLY DURING THE DAY WED...SWINGING
THE SUBSIDENCE WAVE DOWN ACROSS THE REGION EARLIER IN THE DAY ON
THU. THE SFC COLD FRONT WOULD THEN BE MAKING ITS PASSAGE OVER THE
AREA DURING THE FIRST-HALF OF THE DAY THU...ALBEIT VERY SLOWLY.

EVEN W/ THIS GENERALLY MORE PROGRESSIVE SOLN...INSTABILITY WILL BE
AT ITS HIGHEST WED MRNG/AFTN. THE COMBINATION OF LOW LEVEL MOISTURE
AND LOWERED HEIGHTS FROM THE INCOMING UPPER TROUGH WILL MAKE FOR THE
BEST INSTABILITY PROFILES OF THE NEXT COUPLE OF DAYS. THERE WILL BE
A BIT OF A WARM NOSE A FEW THOU FT ABOVE THE BOUNDARY LAYER TO
OVERCOME...SO LAPSE RATES WOULD HAVE TO EITHER STEEPEN QUICKLY OR A
POTENT LOW LEVEL TROUGH OR OTHER FORCING FEATURE WOULD HAVE TO MOVE
THRU. THAT IS JUST WHAT MED RANGE HIGHER-RES MODELS LIKE THE NAM12
ARE INDICATING. SOME PREFRONTAL WAVE-LIKE FEATURES EXTENDING FROM
NEW ENGLAND TO THE LOWER TENN VLY WILL BE SWINGING DOWN ACROSS THE
REGION...KICKING OF BATCHES OF LINEAR AND DISCRETE CONVECTION ALL
ALONG THE WAY. OUR PRECIP ACTIVITY WILL LIKELY BE FAIRLY SCATTERED
IN NATURE THE ENTIRE PERIOD...FROM WED AFTN INTO EARLY THU - THE
BEST CHANCES FOR PRECIP.

DESPITE INCREASING CLOUD COVER ON WED AND THE POTENTIAL FOR
SCATTERED SHOWERS/TSTMS...TEMPS WILL BE THEIR HIGHEST IN SEVERAL
DAYS. HIGHS TOPPING OUT IN THE L-M90S W/ DEWPOINTS NEAR 70 MEAN HEAT
INDICES AT LEAST A COUPLE OF DEG ON TOP OF THE AMBIENT TEMP. A EARLY
MRNG COLD FRONTAL PASSAGE THU MRNG WOULD THEN MEAN A MUCH COOLER THU
FOR THE AREA...NOT ONLY IN TERMS OF THE HIGH TEMPS - IN THE L-M80S -
BUT DEWPOINTS WILL BE SEVERAL DEGREES LOWER. HUMIDITY VALUES WILL
ACTUALLY DECREASE MORE AND MORE AS THE DAY PROGRESSES INTO THE
OVERNIGHT THU AFTN INTO THU NIGHT...W/ A REINFORCING DRIER NW FLOW
PUSHING ACROSS THE REGION BEHIND THE UPPER TROUGH.

FRIDAY THROUGH MONDAY/

A COUPLE OF DAYS OF UPPER TROUGH INFLUENCE TO CLOSE OUT THE
WEEK...WHILE THE FEATURE PASSES BY TO THE NORTH AND KEEPS FAIRLY
QUIET WX ACROSS THE REGION. MEANWHILE...A COMPACT LOW PRES SYSTEM
JUST NORTH OF THE HIGH PLAINS INTO S CNTRL CANADA GEARS UP. THIS
SYSTEM WILL CARRY A LONG-STRETCHED COLD FRONT DOWN ACROSS THE
UPPER-MID MISS VLY FRI-SAT. FAST UPPER ZONAL FLOW WILL PUSH THE
UPPER WAVE INTO THE OHIO VLY DURING THE DAY SAT...W/ THE TAIL END
BRINGING SOME PRECIP CHANCES BACK TO THE AREA SAT NIGHT INTO SUN.
FROM THERE...POTENTIALLY ANOTHER ACTIVE FEW DAYS IF LONG TERM TRENDS
HOLD UP. SEVERAL SMALLER VORTS WELL TO THE NORTH COULD COMBINE AND
SLIDE THESE WAVES DOWN ACROSS THE ERN HALF OF THE CONUS EARLY NEXT
WEEK...BRINGING MORE INSTABILITY AND PRECIP CHANCES TO THE REGION.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
MVFR CIGS OVER MOST OF THE TERMINALS LATE THIS MORNING. CONDITIONS
EXPECTED TO IMPROVE TO VFR IN THE NEXT FEW HOURS. ISOLATED SHOWER
OR MAYBE A BRIEF TSTM PSBL THIS AFTERNOON. WINDS FROM THE
S-SE...LESS THAN 10KT.

SCATTERED SHOWERS AND TSTMS POSSIBLE WED AFTN INTO EARLY THU. AN
OFFSHORE HIGH WILL PUSH UP THE HEAT/HUMIDITY BEFORE TSTMS
ARRIVE/DEVELOP...WHILE A COLD FRONT APPROACHES FROM THE NW. THE
FRONT WILL LIKELY MOVE ACROSS THE AREA LATE WED INTO EARLY
THU...SWEEPING THIS ACTIVITY OFF THE COAST BY LATE THU AFTN. DRY
AND COOLER AIR WILL THEN SWEEP THIS ACTIVITY OFF THE COAST INTO
THE WEEKEND.

&&

.MARINE...
WINDS BLO SCA VALUES TDA/TGNT.

LIGHT S-SW FLOW WILL CONTINUE MID-WEEK AND MAXIMIZE JUST BEFORE THE
PASSAGE OF A COLD FRONT EARLY THU. SHOWERS AND TSTMS POSSIBLE WED
EVE INTO THE OVERNIGHT. OUTSIDE OF CONVECTIVE ACTIVITY...ONLY LIGHT
WINDS ACROSS EXPECTED FOR THE REST OF THE WEEK.

&&

.TIDES/COASTAL FLOODING...
THE DAYTIME HIGH TIDE CYCLE IS THE LOWER OF THE TWO
ASTRONOMICALLY...HENCE THERE WL BE NO NEED FOR AN ADVISORY DURG THE
DAY. WILL CONTINUE TO MONITOR FOR POTENTIAL MINOR FLOODING AT HIGH
TIDE EARLY WEDNESDAY MORNING.

&&

.CLIMATE...
YDA WAS ONE MONTH SINCE THE SUMMER SOLSTICE. WE`RE A LTL OVR
HALFWAY THRU WHAT IS CONSIDERED MET SUMMER. HOW DOES THIS SUMMER
SHAPE UP SO FAR TEMP-WISE? LOOKING AT THE PAST 30 YRS...

6/1-7/21...1984-2014...

STATION AVG MAX  RANK AVG MIN RANK AVG DAILY RANK

DCA       87     12TH    70   6TH     78.5    9TH
BWI       84.3   23RD    64.3 15TH    74.5    19TH
IAD       83.6   23RD    63.6 12TH    73.6    20TH

AN INTERESTING STAT - DCA...AVG LOW TEMPS FOR THE PAST 30 YRS...
FIVE OF THE TOP SIX WARMEST HV BEEN 2010 THRU 2014. RANKINGS:

1 2010 72.1
2 2013 71.6
3 2011 71.0
4 1994 70.9
5 2012 70.2
6 2014 70.0
7 2008 68.9

EVEN IF YOU XTND TO THE ENTIRE DC RECORD - SINCE 1871...2014 RANKS
#7 FOR WARMEST AVG LOW TEMPS FOR THE PD 6/1-7/21.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
NEAR TERM/AVIATION AND COASTAL FLOOD UPDATE...KCS







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