849 
fxus63 keax 222127 
afdeax 


Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
327 PM CST sun Nov 22 2009 


Discussion... 


Precipitation chances during the early portion of the week along with the 
evolution of surface temperatures associated with this system will remain the 
items of most concern for this forecast. 


This afternoon...profiler and WV imagery confirm the presence of a rather 
fast moving upper short wave trough racing through central Kansas at this time. This 
short wave trough is handled well by the deterministic model 
guidance...with the upper trough axis crossing the MO/Kansas state line 
around midnight. Without a large quantity of low-level moisture for 
this system expect the impact to be minimal. Isentropic lift 
remains rather unfocused in nature...but may be strong enough to tap 
into thicker middle-level moisture plume ahead of the short wave in the northern 
and eastern County Warning Area. Will maintain slight chance pop. 


Of other concern in the immediate short term will be the potential 
for patchy dense fog across the northern portions of the County Warning Area. Models 
suggest the development of a weak surface warm front across the 
central County Warning Area by mid-morning. Boundary layer moisture is expected to 
remain rather high overnight. However the amount of clearing and 
middle-level subsidence behind the upper short wave remain in doubt. 
Soundings...numerical guidance...and sref probabilities suggest at 
least MVFR fog with patchy dense fog possible should skies clear 
more than currently anticipated. 


For Monday...next upper wave currently in the Pacific northwest expected to dig 
across the Western Plains by Monday afternoon and quickly pivot NE into the 
Great Lakes by Tuesday night. 12z deterministic models remain in general 
agreement...with the GFS slightly faster and deeper than the 12z NAM 
and European model (ecmwf). The 18z NAM is a distant outlier...with a solution that is 
digging the upper trough to far to the south given the amplitude of the 
kicker wave upstream. Nevertheless...it should be noted that there 
has been a slightly slower and further south trend in deterministic 
guidance during the past 2 model runs and these trends have been 
considered in the current forecast given the strong Pacific jet accompanying 
this system. Ensembles remain supportive of the 12z GFS/European model (ecmwf) solutions 
keeping the overall upper track across central Kansas across northern MO. 
Overall expecting a fairly dry and warm day on Monday as we remain 
stuck in middle-level short wave ridging between upper troughs. Will continue to 
advertise low 60s for temperatures along with a slight chance pop in the northwest 
corner. 


For Monday night and Tuesday...biggest questions arise to just how fast 
this upper trough will eject eastward. By Monday evening strong upper support 
begins to move NE into the area as the system reaches peak intensity. 
However the tilt and intensity of this system remain key to the 
forecast...with current indications of this system approaching the County Warning Area in 
a positive tilt and pivoting over the western County Warning Area Monday night. In 
return this may force two different areas of precipitation...an area of rain 
in northeast quadrant of the upper low supported by pv advection and 
the upper jet in northern Kansas and northwest MO...and a secondary area of precipitation 
further south-southwest over southeast Kansas and southern MO. Additionally...point 
soundings and plan view forecast maps suggest a rapid period of low-level 
warm air advection and Theta-E advection enhancing the 850-600 mb lapse rates enough 
to induce isolated to scattered convection as the primary band moves 
though. 


Depending on the track of the upper low...significant dry slot is 
expected to rotate into the area late Monday night or early Tuesday forcing 
linear area of precipitation quickly out of the are by 12z Tuesday. Moisture is 
expected to wrap around the upper low as a extensive trowal 
develops...this moisture may develop into additional precipitation Tuesday afternoon 
and night. 


Frozen precipitation chances still remain very low with this system despite 
the slightly deeper tracks as suggested by guidance. No cold air will 
be present prior to this systems arrival...and even dynamical 
cooling processes won't be able to overtake the low-level warm air 
present prior to the arrival. I won't rule a rain/snow mixture out in the 
wrap around trowal Tuesday afternoon...especially if some of the colder low- 
level air can be tapped off the Western Plains. However feel given the 
timing of arrival and the fact that the system will be nearly 
vertically stacked doesn't Bode well. 


Forecast low and high temperatures will be a big concern Monday night and Tuesday. A 
slightly slow system will keep surface temperatures well into the upper 40s to 
perhaps low 50s Monday night. Highs on Tuesday will be dictated by the 
speed of the surface front and colder air wrapping in from the SW. Have 
issued a non-Standard diurnal curve...and bumped up Monday night 
readings and lowered tuesdays temperatures. 


Maryland 


Medium range (wednesday through sunday)... 


By the middle of the upcoming work week the Central Plains will be 
under the influence of a northwest flow on the backside of a system 
that will have passed through the plains earlier in the week. Middle 
Range models from the European model (ecmwf) to GFS and Gem...plus many of the 
ensemble members...have all come in line with each other over the 
past several runs...so synoptic scale features are in decent 
agreement. 


Shortwave will descend through the northwest flow Wednesday and 
Thursday helping reload/slow the trough that will be moving east 
across the Continental U.S. Mid-week. Result will be that temperatures should 
be a bit cooler than our going forecast numbers...with normal to 
below normal readings expected through Friday. For the weekend the 
slower trough progression implies that the weekend warm up...with 
the ridge following the trough...could be muted a bit with 
temperatures barely able to climb above seasonally normal values. 
Have adjusted temperatures to reflect this trend...with new numbers 
nearest the mex guidance values. 


Otherwise...as for precipitation...even with the trough slowing 
expectations are that the shortwave in the northwest flow will be 
traversing the region from the northern plains into the Ohio River 
valley rather quickly Wednesday and Thursday. This should limit the 
potential for any precipitation in the forecast area middle week to 
regions of north central and northeast Missouri. Even then... 
thoughts are that slight chance probability of precipitation are all that are warranted at 
this time given moisture concerns and timing. For the weekend...the 
ridge that will be moving in should keep conditions dry. 


Cutter 




&& 


Aviation... 


For the 18z tafs...VFR conditions are expected to remain in place 
through the daytime hours as well as into the evening. Short wave trough 
continues to race eastward across western and central Kansas this 
afternoon...with broad isentropic lift generating light rain showers/sprinkles 
north of the terminals. In addition...modest low-level Theta-E 
advection has resulted in a band of MVFR/IFR stratus across central 
Kansas along a stationary front and surface low. 


This short wave will lift NE through the terminals overnight 
tonight...however isentropic lift does not look strong enough to 
produce anything more than sprinkles...with higher probability of precipitation north of 
kstj. However...later shifts will need to keep an eye on MVFR/IFR 
ceilings to our west with are prognosticated to lift northward along a 
developing surface warm front by 3 am. This front should slowly lift 
northward after daybreak and may produce a 4 to 6 hour span of MVFR 
to perhaps even IFR ceilings...with increasing boundary layer moisture 
trapped along this front also reducing visible into MVFR to perhaps IFR 
categories. Will include a tempo group for this occurrence...with 
reduced visibilities more prevalent at kstj where low-level isentropic lift 
will be the greatest. As upper short wave lifts NE by middle-morning a return to 
VFR conditions would be likely. 


Dux 




&& 


Eax watches/warnings/advisories... 
MO...none. 
Kansas...none. 
&& 


$$ 

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