Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 441 AM EDT Tue Apr 07 2020 Valid 12Z Tue Apr 07 2020 - 12Z Fri Apr 10 2020 ...Southwest U.S.... Days 1-3... A cutoff low off the central CA coast this morning will swing southeast to the southern CA coast through Wednesday...then likely linger over southern CA/Desert Southwest through Friday. All 00Z guidance has a slow, wobbly meander east motion to the system, with the CMC and GFS farther east and the ECMWF farther west. A compromise solution between is given in the QPF/winter forecasts. As the low drifts south through tonight, continued flow of enhanced moisture into southern CA. Snow levels generally 5000 to 6000ft will keep impacts limited to the highest terrain on Day 1. WPC snow probabilities are moderate to high for 8 or more inches for the southern Sierra Nevada, San Gabriel and San Bernardino Mountains. As the low shifts inland Wednesday snow levels drop to 4000 to 5000ft and moist flow continues to reach the Transverse Ranges and southern Sierra Nevada, but from the southeast, providing the typically leeward slopes greater than normal precip including the White Mountains and the ranges of Clark Co NV. Day 2 snow probabilities are moderate to high for 8 or more inches for the aforementioned ranges. Day 3 is less certain with shortwave energy likely ejecting from the stalled parent low in the southwest jet increasing over northwest Mexico. Therefore precip will extend from the parent low into the four corners region with mostly moderate snows for the higher terrain of the same ranges in Days 1/2 as well as southern UT and possibly into southern CO/the San Juans. ...Northeast... Day 3... Northern stream low pressure shifting east-southeast through Ontario Wednesday will be reinforced with a potent shortwave that causes the parent low to occlude and allow secondary surface low formation over the eastern Great Lakes into the Northeast Wednesday night as the system is blocked upstream by a persistent/stalled low over the Labrador coast. Rapid surface low development the occurs with this second low off the New England coast Thursday/Thursday night allowing intense precipitation to wrap around the system. The cold core low will allow snow on the north side of the track with heavy snow expected to develop Thursday over northern NH/northwest Maine and expand/enhance Thursday night across northern Maine. Particularly strong jet streak formation (for this time of year) develops over the Mid-Atlantic Thursday night which will promote Gulf-enhanced moisture wrapping around the system in the warm conveyor belt. There are indications of this system reaching potentially record low surface pressures for April on coastal Maine, making for particularly windy and impactful conditions. Given timing and meridianal track uncertainty this system will need to be monitored closely for further details over the next day. As of now, Day 3 snow probabilities are moderately high for 8 or more inches for northern New Hampshire and across northern Maine. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Bryan