186 FXUS63 KDMX 131821 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 121 PM CDT Wed Mar 13 2019 .UPDATE... Issued at 121 PM CDT Wed Mar 13 2019 Have sent out an update to extend the dense fog advisory through this evening. Have seen some improvement across the east central portions of the forecast area and also into SW/west central Iowa. May still need some adjustments as winds pick up and help to dissipate the fog. However latest guidance suggests that the fog across the far north could linger through tonight, so will be assessing the need for a further extension of the advisory through the afternoon hours. All other forecast elements remain on track with the heaviest of the rain moving through the state currently. Will continue to see flooding concerns as many have already been observed due to poor drainage due to frozen culverts/heavy blocking drainage routes. Also reports of ice jams in several locations. Therefore flood watch to remain in place and many areal flood warnings have been issued with the large swath of rain moving across the area this afternoon. Will continue the wind advisory as they area starting to increase across the south and west, a bit later than expected. May still end up with marginal wind advisory conditions. && .DISCUSSION.../Today through Tuesday/ Issued at 330 AM CDT Wed Mar 13 2019 Very active weather over the next 24 to 48 hours as a negatively tilted upper level trough ejects across the central Plains. At the surface an impressive low pressure center tracks from southeast Colorado and across Kansas. Deep southerly flow ahead of the system feeds an unseasonably moist airmass into the region today, aided by a 60+ knot low level jet. Moisture transport over the top of a melting snowpack has led to the ongoing dense fog across much of the cwa. The lowest visibilities persist into the morning hours before gradually improving, but areas of fog between 1sm to 3sm may linger through much of the day. Gusty winds develop by late morning and afternoon hours as the local pressure gradient tightens in response to the deepening low. Wind Advisory continues for areas generally along and south of I-80 where the strongest gusts should reside. Our next round of rainfall is already ongoing early this morning in a zone of increasing mid- level convergence stretching across Nebraska into western Iowa. Weak elevated instability has supported a few lightning strikes, which will likely continue as the activity drifts off to the north. Strongly diffluent flow aloft will support another round of widespread showers and storms later this morning and afternoon. Heavy rainfall is possible at times as pwats push toward climatological maximums. Some concern that more robust deep convection could generate sporadic gusts near or exceeding severe limits as higher velocity mid-level winds are transported to the surface. However this scenario remains highly conditional due to limited instability. A more unstable environment that may support a severe weather threat looks to hang closer to the low center in KS/NE today. Dry slot punches through the cwa by late Wednesday and brings a lull to most appreciable precip chances. Intense upper level trough and attendant surface low become stacked and begin to weaken as the system crosses the state Thursday. Additional showers develop as more moisture wraps around the south side of the low pressure center. Another push of strong winds develop as the low moves east and forces a cold front through the state. Highest confidence in advisory level winds remains over western Iowa. Falling temperatures bring ptypes into question by late Thursday afternoon and evening. Sporadic loss of ice introduction in the models makes it difficult to discern between freezing rain or snow. Regardless of ptype the qpf intensity should be waning over this period and hopefully limit the extent of any wintry impacts especially considering the gusty wind potential. Best chance to see light snowfall accumulation is generally across northwest and north central Iowa where some impacts to travel are possible late Thursday. Much anticipated dry and seasonable stretch of weather arrives Friday as an expansive area of surface high pressure settles into the region. River flooding issues continue into next week due to runoff from the ongoing precip and widespread snowmelt. && .AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/ Issued at 1213 PM CDT Wed Mar 13 2019 Strong low to lift out of the Rockies into the Plains. Widespread LIFR/IFR visibility and ceilings to persist for much of period across northern TAF locations but southern TAF locations will see improving conditions as a dry slot lifts into the area. Some question as to how far north the improving cigs/vsbys will get so confidence is low on cigs in later periods. The low will lift into NE Iowa by 18Z Thu with clouds/vsbys lowering again on the backside of the low. Precip should be light and strong winds are expected. && .HYDROLOGY... Issued at 330 AM CDT Wed Mar 13 2019 Widespread rainfall in excess of 1" is still possible today as additional rounds of showers and storms move through central Iowa. The heavy rainfall will combine with expected rapid snowmelt to bring an increasing flood threat to much of the state through Thursday. The flood threat will extend beyond mainstem rivers to smaller basins and poor drainage areas as well. Conditions are favorable for the continued development of ice jams, and confidence is particularity high for ice jamming to occur in typically favorable areas within the next 24 to 48 hours. This includes the Des Moines River through Fort Dodge and the Raccoon River from Van Meter to Des Moines. Please continue to pay attention in the coming days for any flood warnings issued by the NWS. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Thursday evening for IAZ004>007-015>017- 023>028-033>039-044>050-057>062-070>075-081>086-092>097. Dense Fog Advisory until 7 PM CDT this evening for IAZ004>007- 015>017-023>028-033>038-044>048-057>060-070>072. Wind Advisory until 7 PM CDT this evening for IAZ057>060-070>075- 081>086-092>097. && $$ UPDATE...Beerends DISCUSSION...Martin AVIATION...FAB HYDROLOGY...Martin