Extended Forecast Discussion NWS Weather Prediction Center College Park MD 319 PM EST Tue Feb 15 2022 Valid 12Z Fri Feb 18 2022 - 12Z Tue Feb 22 2022 1900 UTC Update... The latest 00z/06z model cycle continues to show above average agreement through the entire period on the large scale, with some lingering uncertainties in the smaller scale details which mostly show run to run variability anyways. Models have remained mostly consistent with their previous runs and so, no major changes were needed for todays update to the WPC medium range product suite. The only notable change to previous continuity was a slight northward shift in the QPF axis across the Deep South early next week, although given the longer time range, remains rather uncertain anyways. Todays blend consisted of the updated deterministic model runs for days 3-5, with some incorporation of the ensemble means on days 6-7 to help mitigate the detail differences. See previous discussion below for model evaluation details and associated sensible weather threats. Santorelli Previous discussion issued at 0700 UTC... ...Overview... Low pressure and a strong cold front along with its associated precipitation will be exiting the East Coast on Friday, behind which northern stream energy will push a clipper system with some snow near the Great Lakes region. Then early next week, troughing is forecast to develop in the West and slowly track eastward along with a frontal system. Precipitation chances should increase in the West with this pattern and spread into the central U.S. once again by next Monday and Tuesday, with the possibility of northern tier snow and southern U.S. rain. ...Guidance Evaluation/Predictability Assessment... Recent model guidance shows good agreement overall with the large scale pattern even through early next week, with some typical differences in the smaller scale details. 12Z/18Z models remain fairly well clustered with the strengthening surface low near the Northeast/southeastern Canada early Friday, along with the track and strength of the surface low near the U.S./Canadian border pushing into the Great Lakes region Friday into Saturday. A multi-model deterministic blend of the 18Z GFS and 12Z ECMWF, CMC, and UKMET worked well for these features and kept with continuity well. A somewhat less certain feature during this timeframe is a compact shortwave rounding the ridge in the eastern Pacific that could enter the Pacific Northwest or northern California around Friday night and move eastward, but with some differences in its timing and placement, which may not be resolved for a while given its small scale. However, troughing developing in the West early next week is coming into somewhat better agreement overall with its development, depth, and movement, but there are still notable differences as energy spills in from the low predictability high latitudes. GFS runs have been the strongest with the trough and occasionally close off an upper low, but recent runs have backed off a bit on the strength, closer to the pattern shown by the more consistent ECMWF. Some phasing differences with potential stream separation also are causing minor model differences that could continue to be an issue with the evolution of the troughing. But overall agreement is better than usual considering the forecast time range of 6-7 days. The WPC forecast phased in some GEFS and ECMWF ensemble mean guidance for the latter part of the period, but still kept a majority deterministic model blend throughout given the fairly good agreement currently, with the blending process and some usage of the means taking care of individual model eccentricities. ...Weather Highlights/Threats... As the medium range period begins Friday, rain and snow will mostly be exiting the East Coast along with a low pressure/frontal system, though showers could linger in Florida. Gusty winds could also continue on Friday particularly in the Northeast near the strong surface low. Snow is forecast for the end of the week across the Great Lakes region with the clipper system, with generally light to perhaps locally moderate amounts. Mainly dry conditions are expected elsewhere on Friday, before precipitation starts to increase in the West over the weekend with the upper trough coming in. Coastal and valley rain and mountain snow are likely over the Pacific Northwest spreading into California, the Great Basin, and the Rockies. Snow is possible for the Northern Plains as well by early next week, but with low confidence in the snow axis and amounts at this point. By Monday and Tuesday moist inflow will return from the Gulf of Mexico, increasing rain chances across the Gulf Coast states. The East Coast can expect temperatures to be warmer than average Friday morning, even setting daily records for warm lows, before quickly falling behind the cold front, leading to temperatures right around average for the weekend. Meanwhile, colder than normal temperatures by 10-20F are expected in the south-central U.S. to Midwest on Friday and moderating by Saturday. Temperatures will be warmer than average starting in the Northwest late this week and spreading into the Plains this weekend, and highs in the 60s are forecast by Sunday as far north as Nebraska and western Iowa. Warm temperatures shift/spread to the East Coast early in the workweek while the western half of the nation cools down underneath the trough. The northern and central High Plains could see temperatures 15-25F below normal Monday into Tuesday. Tate Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sat-Sun, Feb 19-Feb 20. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - High winds across portions of the Mid-Atlantic and the Northeast, Fri, Feb 18. - Much below normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Mon-Tue, Feb 21-Feb 22. - Heavy precipitation across portions of the Alaska Panhandle, Fri, Feb 18. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml