NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260921_1200
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)
=== ===== === ==== ==== === === === ====
Mon 09/21 12Z 0.05 0013  96   1   4 0.00
Mon 09/21 13Z 0.09 0014  95   1   3 0.00
Mon 09/21 14Z 0.07 0015  94   1   3 0.00
Mon 09/21 15Z 0.07 0015  91   1   3 0.00
Mon 09/21 16Z 0.07 0013  87   1   4 0.00
Mon 09/21 17Z 0.09 0113  83   1   4 0.00
Mon 09/21 18Z 0.09 0111  80   1   4 0.00
Mon 09/21 19Z 0.09 0111  77   1   4 0.00
Mon 09/21 20Z 0.08 0110  74   1   4 0.00
Mon 09/21 21Z 0.09 0110  70   2   5 0.00
Mon 09/21 22Z 0.08 0111  67   2   5 0.00
Mon 09/21 23Z 0.11 0212  63   2   5 0.00
Tue 09/22 00Z 0.14 0212  60   2   5 0.00
Tue 09/22 01Z 0.16 0312  56   2   5 0.00
Tue 09/22 02Z 0.17 0412  52   2   5 0.00
Tue 09/22 03Z 0.18 0510  50   2   5 0.00
Tue 09/22 04Z 0.17 0509  50   3   5 0.00
Tue 09/22 05Z 0.20 0609  52   3   5 0.00
Tue 09/22 06Z 0.21 0709  54   3   4 0.00
Tue 09/22 07Z 0.17 0806  58   3   4 0.00
Tue 09/22 08Z 0.16 0906  62   3   4 0.00
Tue 09/22 09Z 0.18 0907  63   3   3 0.00
Tue 09/22 10Z 0.12 1004  65   3   3 0.00
Tue 09/22 11Z 0.12 0804  65   3   3 0.00
Tue 09/22 12Z 0.17 0706  63   3   3 0.00
Tue 09/22 13Z 0.18 0607  64   3   3 0.00
Tue 09/22 14Z 0.19 0608  62   3   3 0.00
Tue 09/22 15Z 0.21 0608  63   3   3 0.00
Tue 09/22 16Z 0.23 0607  64   4   3 0.00
Tue 09/22 17Z 0.32 0606  67   4   2 0.00
Tue 09/22 18Z 0.60 0605  67   4   2 0.00
Tue 09/22 19Z 0.75 0606  68   5   3 0.00
Tue 09/22 20Z 0.88 0606  70   5   3 0.00
Tue 09/22 21Z 0.64 0707  72   7   3 0.00
Tue 09/22 22Z 0.49 0708  74   8   3 0.00
Tue 09/22 23Z 0.49 0709  73  10   3 0.00
Wed 09/23 00Z 0.51 0710  71  12   3 0.00
Wed 09/23 01Z 0.53 0812  68  15   3 0.00
Wed 09/23 02Z 0.56 0913  64  18   3 0.00
Wed 09/23 03Z 0.56 0914  62  19   3 0.00
Wed 09/23 04Z 0.51 0914  57  21   3 0.00
Wed 09/23 05Z 0.47 0915  57  22   3 0.00
Wed 09/23 06Z 0.45 0915  53  22   4 0.00
Wed 09/23 07Z 0.44 0815  51  20   4 0.00
Wed 09/23 08Z 0.41 0815  48  19   4 0.00
Wed 09/23 09Z 0.42 0816  46  16   4 0.00
Wed 09/23 10Z 0.43 0817  42  13   4 0.00
Wed 09/23 11Z 0.45 0818  42  11   5 0.00
Wed 09/23 12Z 0.45 0818  41   8   5 0.00
Wed 09/23 13Z 0.47 0919  40   4   4 0.00
Wed 09/23 14Z 0.49 0919  41   4   4 0.00
Wed 09/23 15Z 0.48 0917  44   6   4 0.00
Wed 09/23 16Z 0.50 0915  48   6   4 0.00
Wed 09/23 17Z 0.51 0914  52   7   4 0.00
Wed 09/23 18Z 0.53 0912  54   8   4 0.00
Wed 09/23 19Z 0.59 0911  55   6   4 0.00
Wed 09/23 20Z 0.62 0910  57   5   4 0.00
Wed 09/23 21Z 0.56 0810  57   4   4 0.00
Wed 09/23 22Z 0.50 0811  53   3   4 0.00
Wed 09/23 23Z 0.46 0812  52   2   5 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