Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kind 211143 

Area forecast discussion
National Weather Service Indianapolis in
643 am EST Thu Nov 21 2019

the aviation section has been updated below.


issued at 415 am EST Thu Nov 21 2019

A cold front will move into west central Indiana late this
afternoon and move across the state tonight. Rain showers will
spread across much of the area today but should remain light and
diminish later today. Showers are expected tonight along the front
over south central Indiana. Dry weather moves in on Friday but
another system will approach for Saturday with rain and snow
likely. Yet another strong storm system is expected to impact the
Midwest prior to Thanksgiving. This storm could impact travel
across the country so continue to monitor weather forecasts for
next week if you have travel plans.


Near term /today/...

Issued at 414 am EST Thu Nov 21 2019

Potent short wave over Central Plains will lift northeast today and
help push a cold front through central Indiana late this afternoon
and tonight. Regional radar mosaic shows large area of rain ahead of
cold front moving through Illinois. This will progress into west central
and North Central Indiana this morning before diminishing as forcing
weakens away from parent circulation. Generally categorical to
likely pops west and north today tapering to mid and high chance
south and east with more uncertainty on eastward extent of pcpn. A
strong low level jet is forcing the pcpn early this morning and this
50-60kt low level jet will move across our area today. Forecast
soundings show shallow mixing depths with clouds and pcpn limiting
factors for stronger wind gusts. Would not be surprised to see a few
gusts reach 40 knots if some deeper mixing can be realized. For now
stayed around 30 knot gusts per BUFKIT momentum Transfer. Hrrr 10m
wind gust potential looks much too strong given lack of heating and
shallow mixing.


Short term /tonight through Saturday night/...

Issued at 414 am EST Thu Nov 21 2019

An active and more winter like pattern later in the short term
period. Cold front to push through southeast areas this evening. A
secondary weak wave and moisture surge may reinvigorate showers
along boundary this evening in the south to increased pops once
again. Drier air and Canadian high slide in for Friday. Stayed
optimistic with cloud cover and clearing given very dry air per
soundings. However, expect a rather strong subsidence inversion on
Friday and some potential for trapped stratus once again. Will
rely on strong subsidence and strength of high and lean toward the
clearing skies.

Dry weather will be short lived as upper low over southwest Continental U.S.
Today ejects northeast and approaches for Saturday. Uncertainty
remains high in details as models have a lot of differences with
timing and thermal fields. Pcpn type will be an issue with this
system as cold air deepens during the day and strong dynamics lead
to a changeover to snow. Some freezing pcpn remains possible at
onset but this depends on how fast moisture spreads north late
Friday night. Surface temps expected to fall into upper 20s with
slow eroding near surface cold wedge trapped by high pressure to the
north. GFS much faster bringing pcpn into central Indiana while NAM
much slower. Warm nose aloft spreading over cold sfc wedge would
likely result in some light freezing rain central and north for a
few hours Saturday morning with faster solutions. Not ready to buy
into this quite yet as models, especially GFS, tend to be too fast
with eastward ejection of closed upper lows. Will lean toward slower
arrival and frozen pcpn for now. A period of rain or rain snow
possible Saturday morning before cooling aloft and forcing lead to
changeover to a wet snow. Ratios will be rather low so this should
limit any accums to under an inch and primarily grassy surfaces as
it looks now. Expect details to change next few model iterations as
better agreement develops.


Long term /Sunday through Thursday/...

Issued at 353 am EST Thu Nov 21 2019

An upper short wave will be exiting the area on Sunday and models
show a surface high moving in allowing dry conditions Sunday and

Tuesday, there is general agreement on a deep, wide trough digging
into the central U.S. And propagating eastward. This, along an
associated cold front, will bring in chances of rain Tuesday and
slight chances into Wednesday and Thursday. Tight pressure
gradients are expected with this system which will likely cause
gusty conditions. There remain disagreements on details this far
out such as location of the low, trough axis, and how the system
is going to track. In the latest runs, the Euro shows the low
tracking just south of central Indiana whereas the GFS shows the
low tracking just north and that it will be deeper than the Euro
suggests. These differences are going to lead to uncertainties on
timing and how much precipitation ends up falling. At this point,
confident that there will be rain at some point mid week, which
could bring impacts to Holiday travel, but less confident in the

Colder air and high surface pressure is expected to track across
the area behind the front. Depending on how the low pressure
system transpires Tuesday/ mid-week, another wave could impact the
area at the end of the forecast period.


Aviation /discussion for the 21/12z taf issuance/...

Issued at 626 am EST Thu Nov 21 2019

VFR conditions will start the day but as rain moves in, ceilings
are going to degrade to MVFR to IFR conditions. Can't rule out
isolated LIFR ceilings at times with the rain. Expect gusty
winds and wind shear today as well.

Rain is starting to move in and will continue to affect the area
through tonight. Wind shear will be a concern at the start of the
period with a low level jet overhead and should ease up by this
afternoon. Expect winds shifting from southerly to northwesterly
by the end of the taf period. Wind speeds will start out around 10
kts and increase to 15 to 20 kts with gusts up to 35 kts
throughout today. These will then decrease again tonight to 5 to
10 kts.


Ind watches/warnings/advisories...



National Weather Service Glossary of Abbreviations