Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260426_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 04/26 18Z 0.51 3504 60 17 3 0.00
Sun 04/26 19Z 0.60 0006 61 19 3 0.00
Sun 04/26 20Z 0.68 0006 63 18 3 0.00
Sun 04/26 21Z 0.52 0005 63 21 3 0.00
Sun 04/26 22Z 0.84 0205 64 22 3 0.00
Sun 04/26 23Z 0.41 0205 64 23 3 0.00
Mon 04/27 00Z 0.35 0306 64 20 3 0.00
Mon 04/27 01Z 0.45 0406 64 18 3 0.00
Mon 04/27 02Z 0.53 0407 64 17 3 0.00
Mon 04/27 03Z 0.54 0508 64 16 3 0.00
Mon 04/27 04Z 0.47 0507 65 17 3 0.00
Mon 04/27 05Z 0.44 0507 66 19 3 0.00
Mon 04/27 06Z 0.36 0507 67 23 3 0.00
Mon 04/27 07Z 0.37 0507 67 27 3 0.00
Mon 04/27 08Z 0.36 0607 67 34 3 0.00
Mon 04/27 09Z 0.34 0606 67 38 3 0.00
Mon 04/27 10Z 0.31 0606 68 39 3 0.00
Mon 04/27 11Z 0.34 0606 69 38 3 0.00
Mon 04/27 12Z 0.38 0706 69 37 3 0.00
Mon 04/27 13Z 0.49 0806 70 36 3 0.00
Mon 04/27 14Z 1.25 0905 70 35 3 0.00
Mon 04/27 15Z 1.76 1003 70 38 3 0.00
Mon 04/27 16Z 1.54 1002 68 37 4 0.00
Mon 04/27 17Z 1.04 0900 66 37 4 0.00
Mon 04/27 18Z 1.12 0501 66 35 5 0.00
Mon 04/27 19Z 0.64 0901 66 34 5 0.00
Mon 04/27 20Z 0.86 1001 65 32 5 0.00
Mon 04/27 21Z 1.53 1103 63 28 6 0.00
Mon 04/27 22Z 0.19 1602 64 32 6 0.00
Mon 04/27 23Z 0.30 1403 65 20 6 0.00
Tue 04/28 00Z 0.28 1405 65 16 5 0.00
Tue 04/28 01Z 0.21 1506 64 12 5 0.00
Tue 04/28 02Z 0.19 1507 64 11 5 0.00
Tue 04/28 03Z 0.14 1608 64 10 5 0.00
Tue 04/28 04Z 0.05 1709 63 10 5 0.00
Tue 04/28 05Z 0.04 1708 61 10 5 0.00
Tue 04/28 06Z 0.14 1608 59 9 5 0.00
Tue 04/28 07Z 0.20 1509 61 9 5 0.00
Tue 04/28 08Z 0.25 1511 62 8 5 0.00
Tue 04/28 09Z 0.19 1613 65 8 4 0.00
Tue 04/28 10Z 0.21 1615 65 7 4 0.00
Tue 04/28 11Z 0.10 1715 66 7 4 0.00
Tue 04/28 12Z 0.22 1618 65 8 4 0.00
Tue 04/28 13Z 0.26 1520 66 9 4 0.00
Tue 04/28 14Z 0.39 1520 68 9 4 0.00
Tue 04/28 15Z 0.65 1520 68 9 4 0.00
Tue 04/28 16Z 1.93 1518 68 9 3 0.00
Tue 04/28 17Z 3.02 1616 68 9 4 0.00
Tue 04/28 18Z 3.55 1516 67 9 4 0.00
Tue 04/28 19Z 3.51 1516 68 9 4 0.00
Tue 04/28 20Z 2.99 1516 68 8 4 0.00
Tue 04/28 21Z 2.08 1616 66 7 5 0.00
Tue 04/28 22Z 1.02 1617 65 5 5 0.00
Tue 04/28 23Z 0.18 1718 67 5 5 0.00
Wed 04/29 00Z 0.14 1720 70 6 5 0.00
Wed 04/29 01Z 0.14 1622 70 9 5 0.00
Wed 04/29 02Z 0.05 1821 74 22 5 0.00
Wed 04/29 03Z 0.05 1821 73 31 5 0.00
Wed 04/29 04Z 0.13 1921 76 37 4 0.00
Wed 04/29 05Z 0.20 2020 82 43 3 0.00
Run total areal avg QPF for the greens is: 0.00 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1