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Area forecast discussion 
National Weather Service Wakefield Virginia 
121 PM EDT Friday Mar 19 2010 


Synopsis... 
high pressure remains over the region through Sunday. Low pressure 
approaches from the southwest Sunday night. The trailing cold front 
crosses the area Monday as the low moves into southern New England. 


&& 


Near term /through tonight/... 
the sky is clear across the middle Atlantic region this morning as an 
upper level ridge prevails aloft. Another sunny mild day is 
expected with temperatures warming to the upper 60s along the 
coast and into the 70s inland after a cool morning. Dewpoints will 
continue to be the primary forecast challenge given a dry airmass 
in place. Afternoon dewpoints were lowered a few degrees based on 
regional 12z upper air observations and expected mixing potential 
this afternoon. No updates were necessary to the public forecast. 
However...an updated fire weather forecast was issued to reflect 
lower minimum relative humidity values. 


Previous near term discussion... 
cirrus shield from coastal low moves southeast & away from the forecast area this am as 500 mb 
ridge builds into region from the west. Models shwng weak trough dvlpng in Lee 
of mts this afternoon. This ftr will likely serve to keep winds in a 
north-northwest drctn west of Bay allowing column to further dry. Winds stay north-NE 
along the coast. 850 mb temperatures with full sun sprts high temperatures in the 
l-m70s west of Bay...u60s to near 70 at the coast. Loaded the lower mixed 
layer deep temperatures (m-u2os west of Bay...l30s along the coast) into the grids. 
This results in rh's dropping to near 20% west of Bay...25-30% along the 
coast. This more of a fire weather concern. 


&& 


Short term /Saturday through Sunday/... 
upper level ridge remains in place through weekend. Return flow develops as ridge 
axis slides offshore Sat afternoon through sun. Expect deep temperatures to slowly rise 
into the 30s Sat then between 40-45 sun. 


Sky clear tonite. Lows u30s-l40s. Some afternoon clouds Sat...but still expect a 
M sunny & warm day. Highs l-m70s. M clear to pt cloudy Sat night. Lows in 
the 40s. Models continue to slow the apprch of next systm with any precipitation 
holding off until Sun night. Expect sun to start off pt sunny then become 
M cloudy...but remain dry. Highs l-m70s. 


&& 


Long term /Sunday night through Friday/... 
the extended forecast period will begin unsettled Sun night through at 
least Monday morning...as we see our best chances for a period of rain 
asscd with the northwest-southeast oriented warm/occluded front. Have boosted probability of precipitation 
above 50% during this period...earlier (late sun night) across western 
portions and later (after daybreak mon) over the east. By afternoon...GFS and 
European model (ecmwf) are similar with the depiction of deep...broad dry slotting 
spreading through the forecast region from the SW...as the surface low 
tracks across northern Virginia. Thus have lowered probability of precipitation from SW-NE for Monday 
afternoon...as despite the dry slotting (which in the lower layers would be 
aided by a developing SW or downslope flow)...cannot rule out the 
possibility of convectively-induced showers and/or thunderstorms with the 
daytime heating. As for temperatures...leaned toward an HPC-mex guidance 
blend...I.E. 65-70 for most...which would be predicated on at least 
partial sunshine within the narrow (and departing) warm sector. Even 
with the ensuing cold air advection aloft Monday afternoon...developing SW (donwsloping) 
low level flow will offset and allow for the mild conditions. 


Tuesday...included minimal chances for showers over the northern portions of the 
forecast area asscd with the passage of the middle level low...I.E. Where 
DPVA is most favorable for at least isolated development despite the deep 
SW-west low level flow. Temperatures a bit cooler than Monday...yet still quite mild/ 
seasonable (60-65 for most...cooler along the coasts). 


Wednesday-Thursday relatively uneventful in comparison...at least in terms of 
probability of precipitation. Have maintained dry weather during this time as deep layer ridging 
holds serve across the region (ahead of the next front which would 
most likely not affect the forecast area until Friday at the earliest). 
Temperatures again seasonably mild...60s to lower 70s across the region 
(coolest along the lower eastern shore). 


&& 


Aviation /17z Friday through Tuesday/... 
VFR conditions in store for the taf cycle. Generally clear skies 
will persist through the taf period. Look for mainly a northerly 
flow rather abrupt change in wind direction (easterly) anticipated 
along the coast during the afternoon hours (minor seabreeze)...but 
overall winds should be at or below 10 kts. Winds will diminish a few hours 
after sunset as large dome of high pressure moves overhead. 


Next chance of flight restrictions/precipitation comes Monday into Tuesday as 
a low moves across the area. This could produce some MVFR/IFR 
conditions. 


&& 


Marine... 
marginal Small Craft Advisory for seas continue south of the Virginia/NC border as low pressure 
system off the Carolina coast continues to produce higher NE swells. 
Seas slowly starting to fall along the coast...buoy 2 Michigan off Duck 
still reporting 4 feet seas at 06z Friday. Seas may subside early this 
afternoon...but will continue with early evening ending time with continued 
lingering swells. 


Conditions through the weekend will be marked by sub-Small Craft Advisory conditions 
across all waters as high pressure dominates...with winds generally 
10-15 kts or less and wave heights < 4ft. 


&& 


Fire weather... 
an upper level ridge will continue to prevail over the middle 
Atlantic region through Sunday. A very dry airmass is situated 
underneath the ridge and afternoon minimum relative humidity 
values today and Saturday will plummet to the 15 to 25 percent 
range. A light northwest wind is expected today...which will shift 
to southwest Saturday. An upper level low pressure system 
approaching from the southwest will bring a moistening trend by 
Sunday. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...none. 


&& 


$$ 
Synopsis...mpr 
near term...mpr/ajz 
short term...mpr 
long term...bkh 
aviation...ccw/jab 
marine...ccw 
fire weather... 

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