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Area forecast discussion
National Weather Service Indianapolis in
1245 am EDT Thursday Apr 24 2014
the aviation section has been updated below.
issued at 339 PM EDT Wednesday Apr 23 2014
High pressure will slowly move off to the east tonight allowing more
clouds to move in. A cold front will approach Thursday and move
through Thursday night bringing rain and chances for thunderstorms
on Thursday night. Mostly dry weather will be in place from Friday
through Saturday night with weak upper ridging. A cut off upper low
will meander from the plains to the Great Lakes from Sunday on
bringing chances for rain and below normal temperatures to the area.
Near term /rest of tonight/...
Issued at 938 PM EDT Wednesday Apr 23 2014
Rain /sprinkles/ continues to reach the surface across portions of
Illinois /as close as kcmi so far/ even with dewpoint
depressions of 20 degrees or higher. Short term models continue to
show scattered showers moving across the northern half of the
forecast area through the night.
Believe atmosphere is just too dry for enough rain to reach the
ground to measure a hundredth of an inch...but given what is
happening upstream have decided to add a chance of sprinkles to the
northern half of the forecast area tonight. Gradually spread the
chances from west to east during the night...then ended them from
west to east late tonight as forcing exits.
Previous update increased the sky cover and this still looks good.
Left low temperatures alone for now as there will be breaks in the
sky cover later tonight...but some areas may end up a little above
forecast if thicker cloud cover lingers.
Previous discussion follows...
surface high pressure will slowly shift east tonight but the upper
ridge axis remains upstream until morning. With very dry dew
points...easterly component flow...and dry column under the upper
ridge think models are overdoing precipitation potential tonight across the
north with the forming warm front and kept the forecast dry. Should
see increasing clouds riding over the top of the ridge but that
should be it. Temperature-wise went a little warmer than guidance
with expected increase in cloud cover.
Short term /Thursday through Saturday/...
Issued at 339 PM EDT Wednesday Apr 23 2014
Forecast focus is on probability of precipitation/timing and thunderstorm chances with
Thursday night system. Models are in good agreement and generally
used a consensus approach. This set of runs is even slower with the
arrival of the cold front in the western counties and holds it off
until after 0z...with the NAM as late as 6z and the European model (ecmwf) a slow and
further south outlier with the low center. Thus stuck close to a
NAM/GFS average for timing and only included a low chance from 21z
Thursday-0z Friday. Ramped probability of precipitation up after 0z and included categorical
probability of precipitation across the area from 3-6z with the frontal forcing moving in
and upper forcing moving through along with a 40 knots or so low level
jet ahead of the front bringing moisture up from the Gulf. MUCAPES
of a few hundred are in place ahead of the front and with the
strength of the forcing will continue to include a chance for
thunder ahead of and along the front. Still looks like the front
will be through the area by 12z and thus continuing with dry
forecast for Friday.
Friday night models are hinting at development of a spoke on the
back side of the low moving through the Great Lakes. Right now this
doesn/T look too impressive...but it is showing up in the both the
GFS and NAM and mav probability of precipitation are now in the chance category across the
north. Decided to trend in that direction with a slight chance for
rain in the north. High pressure should be back in place for dry
weather on Saturday.
For temperatures stuck closer to warmer mav numbers for highs based
on projected 850 mb temperatures...and warmer than all guidance for
Thursday night with rain and cloud cover expected.
Long term /Saturday night through Wednesday/...
Issued at 157 PM EDT Wednesday Apr 23 2014
European model (ecmwf) and GFS show quiet weather and ridging across the area on
Sunday and have trended toward a dry forecast at that time.
However there are big changes for the beginning on next week as
both models agree that a large upper low will push out of the
Central Plains and slowly linger over the Ohio Valley through the
middle part of next week. This will bring daily chances for rain
to central Indiana next week along with plenty of clouds and more
below normal temperatures.
Aviation /discussion for the 240600z taf issuance/...
Issued at 1245 am EDT Thursday Apr 24 2014
VFR conditions expected through at least 00z Friday. Light northeast
and east winds overnight will become gusty to around 20 knots from
the southeast Thursday afternoon. Then...winds will shift to west
behind a cold front that should be near ind near 09z Friday. Laf and
huf should see showers move in after 00z Friday...while the threat
will be enough to start at 02z at ind and bmg. Will add thunderstorms in the vicinity to bmg
and huf at the onset with instability a bit higher at those site.
Meanwhile...will hold off for now at laf and ind. Conditions should
deteriorate to MVFR or possibly worse at times after the showers and
or thunderstorms start.
Would not rule out sprinkles overnight out of a 10k ac deck per
radar and observational trends and despite very dry low levels.
May need to add p6sm -shra at last minute if they continue to hang
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