NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251111_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)
=== ===== === ==== ==== === === === ====
Tue 11/11 12Z 0.95 2615  95  25 -10 0.00
Tue 11/11 13Z 1.34 2617  96  27 -10 0.00
Tue 11/11 14Z 2.34 2718  95  31 -11 0.00
Tue 11/11 15Z 2.57 2716  95  43 -10 0.00
Tue 11/11 16Z 2.45 2718  95  60 -10 0.01
Tue 11/11 17Z 3.35 2721  94  76 -10 0.01
Tue 11/11 18Z 4.43 2823  93  79 -10 0.01
Tue 11/11 19Z 4.31 2825  93  85 -11 0.01
Tue 11/11 20Z 2.56 2827  93  85 -11 0.02
Tue 11/11 21Z 1.56 2829  93  82 -10 0.04
Tue 11/11 22Z 1.54 2831  94  83 -10 0.05
Tue 11/11 23Z 1.76 2833  92  82 -11 0.03
Wed 11/12 00Z 2.18 2934  83  35 -11 0.01
Wed 11/12 01Z 1.84 2834  87  22 -11 0.00
Wed 11/12 02Z 1.41 2933  89  25 -10 0.00
Wed 11/12 03Z 1.00 2830  88  28  -9 0.00
Wed 11/12 04Z 0.88 2830  87  30  -8 0.00
Wed 11/12 05Z 0.79 2830  86  26  -8 0.00
Wed 11/12 06Z 0.77 2829  85  26  -7 0.00
Wed 11/12 07Z 0.76 2828  81  29  -7 0.00
Wed 11/12 08Z 0.76 2726  82  26  -7 0.00
Wed 11/12 09Z 0.68 2623  83  40  -6 0.00
Wed 11/12 10Z 0.61 2621  88  73  -6 0.00
Wed 11/12 11Z 0.52 2418  94  87  -6 0.02
Wed 11/12 12Z 0.40 2316  95  89  -6 0.03
Wed 11/12 13Z 0.39 2216  95  92  -6 0.02
Wed 11/12 14Z 0.52 2218  96  94  -7 0.02
Wed 11/12 15Z 0.64 2317  95  91  -7 0.02
Wed 11/12 16Z 0.58 2315  94  89  -7 0.01
Wed 11/12 17Z 0.49 2413  93  90  -6 0.00
Wed 11/12 18Z 0.54 2412  94  88  -6 0.01
Wed 11/12 19Z 0.49 2412  94  89  -6 0.01
Wed 11/12 20Z 0.48 2413  94  89  -6 0.01
Wed 11/12 21Z 0.48 2414  95  90  -5 0.02
Wed 11/12 22Z 0.52 2515  95  90  -5 0.01
Wed 11/12 23Z 0.54 2516  95  88  -5 0.01
Thu 11/13 00Z 0.55 2516  95  90  -5 0.01
Thu 11/13 01Z 0.57 2616  97  87  -5 0.02
Thu 11/13 02Z 0.51 2614  97  87  -5 0.01
Thu 11/13 03Z 0.48 2713  97  88  -5 0.01
Thu 11/13 04Z 0.45 2712  97  88  -5 0.02
Thu 11/13 05Z 0.49 2713  97  85  -5 0.02
Thu 11/13 06Z 0.53 2813  97  82  -5 0.01
Thu 11/13 07Z 0.57 2814  97  79  -5 0.01
Thu 11/13 08Z 0.61 2815  97  80  -5 0.01
Thu 11/13 09Z 0.60 2915  97  82  -6 0.01
Thu 11/13 10Z 0.58 2915  97  85  -6 0.01
Thu 11/13 11Z 0.57 2915  97  88  -6 0.01
Thu 11/13 12Z 0.59 2916  98  88  -6 0.02
Thu 11/13 13Z 0.61 2916  97  88  -6 0.02
Thu 11/13 14Z 0.65 2916  97  88  -6 0.02
Thu 11/13 15Z 0.73 2915  96  88  -7 0.01
Thu 11/13 16Z 1.11 2915  96  89  -7 0.01
Thu 11/13 17Z 1.06 2815  96  89  -7 0.01
Thu 11/13 18Z 1.12 2814  96  85  -7 0.02
Thu 11/13 19Z 1.01 2716  96  86  -6 0.02
Thu 11/13 20Z 1.12 2918  95  88  -7 0.02
Thu 11/13 21Z 1.11 2920  95  86  -7 0.02
Thu 11/13 22Z 0.96 3022  96  82  -7 0.02
Thu 11/13 23Z 0.97 3023  96  82  -7 0.02

Run total areal avg QPF for the greens is: 0.74 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