Area forecast discussion
National Weather Service Indianapolis in
430 PM EDT sun may 19 2013
Update...
the aviation section has been updated below.
&&
Synopsis...
issued at 224 PM EDT sun may 19 2013
A large upper low currently over the plains is expected to bring
unsettled weather to the area through Thursday as it slowly moves
east and weakens with time. High pressure is expected to build in
behind this system towards the end of the week. Another frontal
system may approach the area by next Sunday.
&&
Near term /tonight/...
issued at 224 PM EDT sun may 19 2013
Model data suggest fairly strong 850mb warm advection will be
developing across the area by late tonight as a 40-45kt low level
jet is prognosticated to nose towards into western Indiana by sunrise
Monday. Some concern that this may lead to some elevated convection
during the pre dawn hours of Monday given the very steep middle level
lapse rates expected over the area. Models indicate some enhanced
moisture in the precipitation bearing layer as well. At this
point...Don/T think coverage/potential is high enough for a
mention in the forecast...so will keep the forecast dry.
Low level thicknesses forecasts generally support the GFS MOS lows
tonight...so little adjustment to the guidance.
&&
Short term /Monday through Wednesday/...
issued at 224 PM EDT sun may 19 2013
Main feature during this period will be the large upper low over the
plains that is expected to gradually open up and move into the
Midwest by Wednesday...keeping the short term unsettled.
Some of the finer scale models suggest there may some sort of
boundary...possibly originating from convective activity to the
west tonight...that may move into the area around midday on
Monday. Air mass is prognosticated to become very unstable on
Monday...Li/S down to about -8...underneath steep middle level lapse
rates. Will go with chance probability of precipitation starting around midday and on into
the afternoon.
After Monday...details become a bit more murky as rounds of
convection associated with this system may tend to blur the cold
front position. Model data suggest actual cold front may not move
through until Wednesday night or later. Model data does suggest
lapse rates gradually become poorer with time as air mass gets
worked over...although deep layer shear may tend to increase some
towards Tuesday and Wednesday. At this point...can/T really pin down
any periods to concentrate probability of precipitation on...so with broadbrush high chance
probability of precipitation from Monday night through Wednesday.
Prognosticated low level thicknesses suggest the GFS MOS highs for Monday
and Tuesday may be a bit on the warm side...especially with the
potential for convection or its remnants around. Will nudge the
highs down a bit. Lows look OK.
&&
Long term /Wednesday night through Sunday/...
issued at 224 PM EDT sun may 19 2013
European model (ecmwf) and GFS both indicate a frontal boundary and associated upper
trough exiting the region on Wednesday night and early on Thursday. A
strong ridge aloft then builds across the Ohio Valley for Friday and
Saturday from the Central Plains along with cooler and dry northwest flow.
Thus will keep some chances for thunderstorms and rain on Wednesday night and rain showers on
Thursday in the cyclonic flow on Thursday. However dry weather will
be expected as the work week concludes on Friday along with temperatures at
or only slightly above normals.
European model (ecmwf) hints at a warm front and a weak short wave wave pushing into the
area on Sunday and for now have included some low chance probability of precipitation.
&&
Aviation /discussion for the 192100z ind taf update/...
Issued at 430 PM EDT sun may 19 2013
Raised winds to 9 knots per trends...otherwise no changes.
Previous discussion follows...
VFR conditions will be expected the next 12 hours. Some MVFR or
IFR visibilities will be possible overnight due to diurnal fog. A
return to VFR is expected quickly by 14z Monday as heating and
mixing resumes.
A warm and moist air mass remains in place across central Indiana
today with dew points in the middle 60s. Convective temperatures
will be reached this afternoon and cumulus rule suggests scattered cumulus. With
ccls near 3500 feet...any brief ceilings will be VFR.
After heating is lost...expected clearing skies. However with
light winds and high dew points in the area along with little
change in the overall airmass from the past few days...have
trended toward some persistence type fog overnight. Again, once
heating resumes on Monday morning...diurnal fog will quickly burn
off.
&&
Ind watches/warnings/advisories...
none.
&&
$$
Synopsis...jas
near term...jas
short term...jas
long term....puma
aviation...jp/mk
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