Sunday, March 21, 2010

Rainy Days and Mondays

This is probably a good time to look ahead at the conditions forecast for tomorrow morning's flight from KVKX up to Bridgeport. There is weather on the way, in the form (see left) of a fairly large and vigorous low pressure system currently making things wet in Tennessee and Alabama.

Here's the big picture, the forecast of fronts and precipitation for 12Z tomorrow morning from the NWS Hydrometeorological Prediction Center. This is about the time I plan to get off.

It's worth noting that the chart suggests convective activity deep within the precipitation area, but the conditions for the DC area look to be pretty benign.

As always at this time of year, the key question is, "Where's the freezing level?" The map below, from the Aviation Weather Center site, shows the 5C isotherm right over DC at the 800mb pressure level. That corresponds to 6,000 feet MSL. This map suggests that temperatures at 5,000 feet MSL along the route up to KBDR should be comfortably above freezing.

This is important enough to crosscheck with another source. The nice folks at Wunderground have a freezing level chart for 12Z tomorrow (see left) that also gives confidence that icing won't be an issue. For most of the route it looks like the freezing level will be at 8,000 to 9,000 feet MSL.

The Terminal Area Forecasts (TAF's) say that there will be some weather, but nothing too nasty. For departure, I look at both National (KDCA) and Andrews AFB (KADW):

KDCA 211732Z 2118/2218 16009KT P6SM SCT120 BKN250
FM211900 19011G16KT P6SM SCT140 SCT200
FM212300 17007KT P6SM SCT120 BKN150
FM220400 14004KT 6SM BR VCSH FEW015 SCT025 OVC070
FM220700 12004KT 5SM -RA BR SCT008 BKN015 OVC025
FM221100 12008KT 2SM RA BR SCT004 BKN006 OVC009
FM221600 12011G17KT 3SM -RA BR FEW003 BKN008 OVC011

KADW 2118/2217 20012G18KT 9999 SCT100 QNH2995INS
BECMG 2123/2124 17009KT 9999 BKN100 OVC220 QNH2986INS
BECMG 2208/2209 14009KT 6000 -RA SCT010 OVC025 WSCONDS 650905 QNH2975INS
TEMPO 2213/2217 14012G18KT 3200 RA BR OVC009 T25/2120Z T11/2210Z

So for a 12Z departure, National is expecting 2 mile visibility in rain and mist with scattered clouds at 400 feet AGL and a broken ceiling at 600, winds from the southeast at 8 knots. Andrews is looking for a mile in light rain, scattered deck at 1,000 feet, overcast at 2,200 feet and southeasterly winds at 9 knots.

The TAF for Andrews does contain "WSCONDS", meaning "Wind Shear Conditions" - there will be some strong winds aloft. As the map at left from Aviation Weather Center indicates, the cyclonic winds wrapped around the low at about 6,000 feet will be bumping 50 knots over the South Carolina coast, and will be 20 to 25 knots along my route of flight. As a tailwind!

The TAF for Bridgeport (KBDR) looks fine:

KBDR 211925Z 2119/2218 09010KT P6SM FEW150 SCT250
FM212100 13011KT P6SM BKN150
FM220100 10004KT P6SM SCT050 BKN150
FM220900 13004KT 4SM BR BKN025 OVC100
FM221200 11006KT 4SM BR BKN015 OVC025
TEMPO 2212/2216 3SM -RA BKN010

On arrival at about 14Z I should find 4 miles visibility in mist and a broken ceiling at 1,500 feet with wind from the east at just 6 knots. The ILS for runway 6 will probably be on offer.

At this point, FltPlan.com is telling me to anticipate 1 hour + 44 minutes en route. A quick trip!


DeAnn said...

Very good look at the weather! Impressive.

Frank Van Haste said...

Thanks, DeAnn. It may have been a good look at the weather, but in the event, other weather happened. In my next post I'll tell y'all about the diversion.