HAMweather.com Area Forecast Discussion for County Warning Area EAX

Thu, 16 Feb 2012 11:38:27 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
525 AM CST Thu Feb 16 2012

...UPDATED AVIATION DISCUSSION...

.DISCUSSION...

Short Range (Today through Saturday)...

Looking at water vapor imagery early this morning, three notable 
shortwaves are seen which will control the weather across Kansas and 
Missouri though Saturday. The first noted shortwave is the one which 
brought the rain Wednesday and is about half way through Missouri at 
this time, while a second shortwave is noted cutting off across 
southern California, and a third is seen dropping south southeast 
from the Plains of Canada. 

The first wave will have minimal impact today, so our focus is on 
the second two. Models are in a bit of disagreement on how to eject 
the southern California cutoff through the Plains. GFS in the past 
several runs has shown signs of wanting to phase the cutoff with the 
Canadian Plains shortwave as they traverse the Central Plains Friday 
night into Saturday, bringing the threat of showers as far north as 
central Missouri. GEM is holding to the idea that the waves wont 
quite phase, so the cutoff ejects across the southern Plains. 
Meanwhile the NAM and ECMWF splits the difference, but leave the 
precipitation potential just outside our forecast area. Have opted 
to trend towards the split solutions offered by the ECMWF and NAM as 
the GFS has a tendency to phase shortwaves too much, and squeeze
precipitation out when cloud cover is all that is realistic.

For Today: The first shortwave is only of importance cause its 
leaving, and besides the associated rain shifting east with it, the 
cold front with the passing shortwave is sweeping aside the fog that 
had begun developing across central Missouri overnight. However, the 
surface high behind the front sweeping though this morning is not 
particularly cold owing to its Pacific origins. This will allow 
temperatures today to once again range above normal for 
mid-February. 

Friday: The weak, and merely cool, surface high from Thursday will 
be shifting to the east, allowing a modest warming return flow to 
develop across eastern Kansas and Missouri. This, in combination 
with plenty of sunshine, will lift afternoon highs into the 50s for 
most areas outside of northwest and north central Missouri, where 
highs will likely range through the upper half of the 40s. 

Saturday: The Canadian shortwave will be swinging through the Lower 
Missouri River Valley, bringing a modest cold front to the region.
The origin of this surface high will be a little cooler than the one
moving through today, so have knocked temperatures back down for
Saturday. Generally going with values near the cooler end of
guidance numbers, which corresponded well with the MAV guidance.
Otherwise, have included the merest strip of slight chance POPs
across east central Kansas and west central Missouri for the
fleeting potential that a few drops fall from the mid level clouds
that will be spreading across southern Missouri.

Cutter

Medium Range (Sunday through Monday)...

GFS/ECMWF depict similar features through Tuesday. The upper flow is 
characterized by a progressive pattern featuring shortwave ridging 
moving east through the Plains at the start of the forecast followed 
by a complex upper trough that slogs its way through the 
Southern/Central Rockies and adjacent Plains Monday and Tuesday. The 
slowness and positive tilt of the upper trough necessitates keeping 
at least low chance pops for a prolonged period from Monday through 
Tuesday night. Periods of overall mid level warm air advection 
should result in considerable cloud cover across the forecast area. 
As has been the case all winter there will be a lack of cold air 
intrusions during this period as systems are originating from the 
Pacific Ocean. The overall thermal profile over the CWA suggests the 
precipitation will be all liquid.   

The upper ridge axis will likely enter the CWA late on Sunday 
allowing the mid level warm air advection to spread into the 
region. The GFS/ECMWF both show a piece of shortwave energy ejecting 
out of the initially negatively tilted upper trough and lifting 
northeast through KS and OK on Monday. This feature combined with 
warm air advection should be able to generate some rain showers 
downstream. However, initial low level moisture return will be 
modified due to surface high pressure ridging into the northern Gulf 
of Mexico into Monday. So eastward extent of rain will be limited.

A stronger feed of energy will be diving southward on the backside 
of the upper trough as the initial wave ejects northeast. These two 
features will act to elongate the upper trough and result in a 
positively tilted trough by Monday. This will slow down the overall 
eastward translation of the upper trough and require keeping low 
chance pops in the forecast through Tuesday night. Overall, there 
are only minor day-today changes in the pops from Monday through 
Tuesday night.

With the ECMWF and GFS diverging on their solutions for Wednesday 
have some concern that the upper trough may still be lingering over 
the CWA. For now will continue using a model consensus although 
confidence on Wednesday forecast is lacking. Temperatures will be 
decidedly above average each day.

MJ

.AVIATION...

For the 12Z TAFs...once some light mist burns off this morning,
expect VFR conditions to prevail through the rest of this TAF cycle.
Surface wind will back from northwest to southwest this evening as
the surface high shifts east, but speeds will remain at or below 10
knots. 

Cutter

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.