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000
fxus63 klot 221740
afdlot
area forecast discussion
national weather service chicago/romeoville il
1130 am cst sun nov 22 2009
. discussion...
329 am cst
short term fog concerns and evolution of mid week storm system
continue to be the foci for this forecast package.
this morning ... surface ridge that gave the area a beautiful saturday
continues to shift off to the east. calm winds and generally clear
skies are still in place over the region ... and areas of fog have
once again formed this morning. dewpoint depressions are a few
degrees larger this morning as opposed to last ... and as a result
visibilities have generally stayed in the 3 - 5 sm range ... and really
don`t expect vis to drop too much more this morning.
after any residual fog burns off by mid morning ... today looks to
be a near repeat of saturday ... save for perhaps a bit more mid and
high level cloud cover ... especially across the western
counties ... as warm air advection continues to organize off to the
south and west of the forecast area.
cloud cover will steadily increase tonight and monday morning from
the
west as previously advertised storm system takes shape over
western high plains. numerical guidance has come into
considerably better agreement within the last 24 hours regarding
the evolution of this system. appears that a lead shortwave will
begin to move northeast toward the area during the day monday. at
this time ... looks as if dry easterly flow will keep rain chances
with this first wave to below slight chance mention.
on tuesday ... main area of rain in association with an occluded
front is expected to start moving across the area from southwest
to northeast. rain should expand across the entire forecast area
by tuesday night and early wednesday morning as parent upper
trough traverses the area. thermal profiles tuesday and during the
early morning wednesday appear to be too warm to support anything
other than just rain. secondary shot of cold air associated with
yet another shortwave/upper low will begin to move through the
area wednesday afternoon and evening. as colder air spills south
across the area ... expect precipitation to change to a rain/snow
mix before transitioning to all snow by early thursday morning.
scattered snow showers appear to be possible through thanksgiving
day as upper low continues to spin across upper great lakes. at
this time ... while thermal profile looks to be cold enough to
support snow ... surface temperatures are expected to be warm enough
to preclude anything in the way of significant accumulations.
little change made to forecast for friday through sunday. a few
snow showers look to remain possible across portions of the area
friday with the area situated under cold cyclonic flow aloft.
depending on exact track of trough and surface features ... also
couldn`t
rule out a few light lake effect snow showers across portions of
porter county indiana on friday.
boxell
&&
. aviation...
1130 am cst
1800z tafs ... large high pressure ovr stlawr vly will maintain a
ridge swwd to mid ms vly. though this ridge will gradually erode as
short wave now ovr cntrl plains apchs area tonight ... light sely sfc
flow will continue. skies are expected to remain genly clr until
late tonight when some mid lvl cloudiness assd with wave to w begins
to overspread portions of nrn il. overall though ... conditions
tonight are not expected to be too different from what thery were
last night. as a result ... main wx problem next 24 hrs will be fog
development again overnight and early mon morning. potl is there
for some lifr vis ... but expect these conditions to be confined to
rural area of nrn il/nwrn indiana. clouds to incr monday morning as
sys to w ejects newd through upr midwest as deeper troffing develops
ovr plains stas.
merzlock
&&
. marine...
638 am cst
continued eastward progression of broad surface anticyclone across
southeast canada into northeast united states will result in
slightly strengthening surface pressure gradient across western
great lakes region today ... most notably across northern half of the
lake with a weak sfc ridge axis expected to linger across southern
portions of the lake. expecting light south winds to generally
increase into 10 to 15 kt range this morning ... with some gusts to
around 20 kt this afternoon across northern part of the lake. on
monday ... an area of surface low pressure will begin to take shape
across the central plains and will eventually approach southern lake
michigan on wednesday. this system will begin to occlude
wednesday/thursday which will result in sfc low developing further
back into cold air west of the lake. as upper level system begins to
pull out late thursday ... sfc low will track into eastern great
lakes ... with winds shifting to the northwest and more gusty in
nature in cold advection and stronger gradient behind this system.
marsili
&&
. lot watches/warnings/advisories...
il ... none.
in ... none.
lm ... none.
&&
$$