NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260615_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)
=== ===== === ==== ==== === === === ====
Mon 06/15 18Z 2.48 2911  93  18   7 0.00
Mon 06/15 19Z 2.42 2912  91  16   7 0.00
Mon 06/15 20Z 3.22 2913  89  19   7 0.00
Mon 06/15 21Z 2.27 2916  90  25   7 0.01
Mon 06/15 22Z 1.05 2918  93  25   7 0.01
Mon 06/15 23Z 0.83 3021  95  28   6 0.01
Tue 06/16 00Z 0.81 3022  95  22   6 0.01
Tue 06/16 01Z 0.72 3021  93  23   6 0.01
Tue 06/16 02Z 0.70 3021  94  24   5 0.01
Tue 06/16 03Z 0.59 3121  92  25   5 0.00
Tue 06/16 04Z 0.61 3123  90  26   5 0.00
Tue 06/16 05Z 0.63 3123  95  31   5 0.00
Tue 06/16 06Z 0.65 3122  95  25   4 0.01
Tue 06/16 07Z 0.59 3222  95   8   4 0.00
Tue 06/16 08Z 0.60 3120  96   4   4 0.01
Tue 06/16 09Z 0.47 3218  93   7   4 0.01
Tue 06/16 10Z 0.37 3218  87  12   5 0.00
Tue 06/16 11Z 0.31 3216  82  18   5 0.00
Tue 06/16 12Z 0.29 3113  82  21   5 0.00
Tue 06/16 13Z 0.33 3112  84  30   6 0.00
Tue 06/16 14Z 0.44 3012  84  37   6 0.00
Tue 06/16 15Z 1.66 3011  81  37   6 0.00
Tue 06/16 16Z 3.14 2910  77  42   7 0.00
Tue 06/16 17Z 4.47 2809  73  44   7 0.00
Tue 06/16 18Z 5.43 2709  72  45   8 0.00
Tue 06/16 19Z 5.95 2609  73  44   8 0.00
Tue 06/16 20Z 5.57 2509  73  41   9 0.00
Tue 06/16 21Z 4.76 2509  73  41   9 0.00
Tue 06/16 22Z 2.91 2409  73  39   9 0.00
Tue 06/16 23Z 1.08 2309  71  31   9 0.00
Wed 06/17 00Z 0.63 2310  66  31   9 0.00
Wed 06/17 01Z 0.67 2312  64  29   9 0.00
Wed 06/17 02Z 0.75 2414  65  27   9 0.00
Wed 06/17 03Z 0.77 2514  67  32   9 0.00
Wed 06/17 04Z 0.75 2614  68  31   9 0.00
Wed 06/17 05Z 0.66 2613  70  24   9 0.00
Wed 06/17 06Z 0.62 2611  70  25   8 0.00
Wed 06/17 07Z 0.51 2509  71  26   8 0.00
Wed 06/17 08Z 0.43 2408  71  23   8 0.00
Wed 06/17 09Z 0.35 2308  72  26   8 0.00
Wed 06/17 10Z 0.30 2207  72  26   8 0.00
Wed 06/17 11Z 0.31 2108  72  26   8 0.00
Wed 06/17 12Z 0.34 2108  73  27   8 0.00
Wed 06/17 13Z 0.68 2006  75  25   8 0.00
Wed 06/17 14Z 0.77 1905  76  22   8 0.00
Wed 06/17 15Z 0.42 1705  75  18   9 0.00
Wed 06/17 16Z 0.46 1705  76  15   9 0.00
Wed 06/17 17Z 0.30 1706  77  16   9 0.00
Wed 06/17 18Z 0.34 1707  76  12   9 0.00
Wed 06/17 19Z 0.49 1708  75  10  10 0.00
Wed 06/17 20Z 0.29 1808  73  11  10 0.00
Wed 06/17 21Z 0.35 1808  72  14  10 0.00
Wed 06/17 22Z 0.26 1809  71  11  11 0.00
Wed 06/17 23Z 0.07 1810  71  13  11 0.00
Thu 06/18 00Z 0.06 1711  71  20  11 0.00
Thu 06/18 01Z 0.17 1913  72  23  11 0.00
Thu 06/18 02Z 0.24 1915  72  26  11 0.00
Thu 06/18 03Z 0.24 1916  75  31  10 0.00
Thu 06/18 04Z 0.50 2020  79  32  10 0.00
Thu 06/18 05Z 0.43 2021  82  39  11 0.00

Run total areal avg QPF for the greens is: 0.09 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