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Displaying AFOS PIL: AFDDMX Received: 2017-11-14 23:32 UTC
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557 FXUS63 KDMX 142332 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 532 PM CST Tue Nov 14 2017 .SHORT TERM.../Tonight through Wednesday/ Issued at 322 PM CST Tue Nov 14 2017 12z KOAX RAOB sampled a strong inversion/environmental mixed layer (EML) around 850mb with a moisture rich environment beneath it. Early afternoon GOES-16 Day Cloud Phase Distinction RGB showed plenty of low clouds with some passing higher clouds over the state. Surface observations and Iowa DOT webcams show areas of fog with visibilities reduced the most over far south central and north central Iowa early this afternoon. These clouds and fog will remain as well as pockets of drizzle as a strong PV anomaly moves out of the northern Rockies late this afternoon to the western Great Lakes by tomorrow night. At the surface, low pressure will move from central South Dakota to over Lake Superior tonight with a cold front moving across the state. This front will bring increased forcing with plenty of moisture persisting beneath the EML. The strongest omega will be within or near the top of the EML so expect only scattered, short-lived light rain showers overnight. By daybreak Wednesday, the front will be moving through eastern Iowa with colder and drier air advecting into the state. Clouds will break as the colder air erodes the inversion with mechanical mixing also aiding in this effort. Cross sections across central Iowa from the NAM, GFS, and ECMWF all show a decrease in depth of the high moisture. The NAM remains aggressive with high RH values greater than 85% below 850mb while the GFS/ECMWF have a small layer of RHs roughly greater than 60%. This is most true over northern Iowa and have left in few to scattered clouds. Otherwise, gusty winds from the northwest will develop behind the front and have increased winds several knots. High pressure will begin to ease the winds late in the day as it starts to arrive from the Dakotas and Nebraska. .LONG TERM.../Wednesday night through Tuesday/ Issued at 322 PM CST Tue Nov 14 2017 ./Wednesday Night through Saturday/...Confidence Medium Main challenge will be system from Thursday through Saturday. At this time the models are in fairly good agreement with regard to most of the features...though suspect there may be a few minor changes moving forward. Before the arrival of the end of week system...a secondary Arctic boundary will move south into northern Iowa Wednesday evening before retreating by Thursday morning as a weak ridge of high pressure slides east across the region Thursday. Forecast mins Thursday morning may be impacted by clouds over the west and may result in slightly warmer readings if mid to high level clouds return quickly enough prior to 12z. Otherwise a northern stream shortwave tracking into Manitoba by 06z Friday will pull the warm front northeast with time...with milder air returning to the region late Thursday into Friday. Meanwhile farther west the large scale trough digging into the west coast will amplify somewhat as it progresses east with time. Clouds...strong warm air advection and rain showers will increase Friday. Instability also increases during the day over the southeast...and soundings support some elevated convection mainly over the far southeast during the day/evening hours as a sfc low tracks into the region. The models have been in very good consistency regarding the flow remaining generally non phased...or split through this event. The lack of strong cold air advection following the first northern stream wave will allow the southern stream system to track east with little northerly amplification into Friday night/Saturday. Even though that is true...the Euro and to a lesser degree the GFS bring in enough cold air Friday night to create a brief rain/snow mix...possibly changing briefly over to all snow as the system departs. At this time...any impacts that might occur appear to be minor. By Saturday afternoon both the GFS and Euro continue to show sufficient cold air advection to keep afternoon highs rather cold over the area. There is still some uncertainty as to how fast we will clear out in the afternoon with the Euro slightly slower. With that trend have kept afternoon highs closer to the lower end of ensemble guidance at this time. Brisk northwest winds will lower wind chills to the upper teens over the north by late afternoon...so any outdoor events will feel quite cold by late day. ./Saturday Night through Tuesday/...Confidence Medium to High Once the system exits to the east...clearing is anticipated for at least part of Saturday night. The past two runs of the Euro are already showing return clouds overnight into Sunday morning due to upstream warm air advection processes over the Dakotas. This is happening despite an area of high pressure moving into the area. Min temps are somewhat in question...especially if the cloud cover returns sooner. The current forecast is tilted toward the lower end of guidance...but may need to be raised by about 4 degrees most areas if clouds arrive earlier in the night on Saturday. The remainder of the forecast is quiet with high confidence on a warming trend with virtually no precipitation expected. With a flatter more zonal flow in store for the area Monday and Tuesday...a recovery in forecast temperatures is in the offing. Highs Monday and Tuesday given H850 temps in the single digits south...should recover to the mid to upper 40s south...while the north holds onto 30s to lower 40s for the 2 day period. The beginning of the Thanksgiving holiday travel period (Tuesday) at this time looks benign in the Central Plains as storms continue along the east and west coasts but ridging high pressure continues here. && .AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/ Issued at 532 PM CST Tue Nov 14 2017 Areas of drizzle and fog reducing visibilities across portions of the area to around 3 miles to less than a mile in spots this evening. Some rain showers to develop later tonight which may help lift visibilities. Winds to shift around northwest toward early Wednesday, with LIFR/IFR CIGS lifting or clearing out into Wednesday morning. WIll have to monitor as the clouds could linger longer in the north/northeast through the day Wednesday. && .DMX WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until midnight CST tonight for IAZ007-017- 026>028. && $$ SHORT TERM...Ansorge LONG TERM...REV AVIATION...Beerends