NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260830_0000
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 08/30 00Z 0.59 2512  78  17  10 0.00
Sun 08/30 01Z 0.72 2514  79  16  10 0.00
Sun 08/30 02Z 0.83 2517  79  19  10 0.00
Sun 08/30 03Z 0.93 2619  73  30  10 0.00
Sun 08/30 04Z 1.02 2621  70  39  10 0.00
Sun 08/30 05Z 0.96 2622  69  51  11 0.00
Sun 08/30 06Z 1.04 2727  75  61  11 0.00
Sun 08/30 07Z 1.11 2730  82  70  11 0.00
Sun 08/30 08Z 1.12 2730  84  66  11 0.00
Sun 08/30 09Z 1.05 2829  84  52  11 0.00
Sun 08/30 10Z 0.88 2826  84  48  11 0.02
Sun 08/30 11Z 0.83 2824  85  54  11 0.01
Sun 08/30 12Z 0.76 2823  86  62  11 0.02
Sun 08/30 13Z 0.71 2821  86  66  11 0.01
Sun 08/30 14Z 0.67 2719  87  68  11 0.01
Sun 08/30 15Z 0.68 2618  86  60  11 0.00
Sun 08/30 16Z 0.78 2618  86  65  11 0.01
Sun 08/30 17Z 0.94 2618  86  66  11 0.02
Sun 08/30 18Z 1.02 2620  85  70  11 0.02
Sun 08/30 19Z 1.25 2620  83  85  11 0.02
Sun 08/30 20Z 1.03 2520  84  90  11 0.02
Sun 08/30 21Z 1.31 2623  90  92  11 0.10
Sun 08/30 22Z 1.09 2724  92  91  10 0.08
Sun 08/30 23Z 0.94 2824  89  88  10 0.02
Mon 08/31 00Z 0.81 2923  89  84  10 0.01
Mon 08/31 01Z 0.65 3021  94  74  10 0.01
Mon 08/31 02Z 0.50 3120  93  70  10 0.01
Mon 08/31 03Z 0.40 3218  92  61  10 0.01
Mon 08/31 04Z 0.33 3216  91  50  10 0.01
Mon 08/31 05Z 0.29 3215  89  39  10 0.02
Mon 08/31 06Z 0.21 3315  85  32  10 0.02
Mon 08/31 07Z 0.20 3314  84  20  10 0.01
Mon 08/31 08Z 0.16 3312  79   8  10 0.01
Mon 08/31 09Z 0.16 3312  80   8  10 0.00
Mon 08/31 10Z 0.13 3310  76  10  10 0.00
Mon 08/31 11Z 0.13 3309  75  10  10 0.00
Mon 08/31 12Z 0.11 3308  72   6  10 0.00
Mon 08/31 13Z 0.12 3207  70   7  10 0.00
Mon 08/31 14Z 0.12 3206  71   9  10 0.00
Mon 08/31 15Z 0.11 3104  71   9  10 0.00
Mon 08/31 16Z 0.11 3003  72   8  10 0.00
Mon 08/31 17Z 0.18 2703  75   7  10 0.00
Mon 08/31 18Z 0.29 2705  74   7  10 0.00
Mon 08/31 19Z 0.31 2605  71   8  11 0.00
Mon 08/31 20Z 0.26 2604  69   9  11 0.00
Mon 08/31 21Z 0.24 2603  69   8  11 0.00
Mon 08/31 22Z 0.22 2504  70   8  11 0.00
Mon 08/31 23Z 0.20 2404  70   9  11 0.00
Tue 09/01 00Z 0.17 2504  71  12  11 0.00
Tue 09/01 01Z 0.11 2503  72  16  11 0.00
Tue 09/01 02Z 0.12 2403  73  20  11 0.00
Tue 09/01 03Z 0.10 2303  74  22  11 0.00
Tue 09/01 04Z 0.09 2303  76  20  11 0.00
Tue 09/01 05Z 0.07 2103  78  26  11 0.00
Tue 09/01 06Z 0.06 2103  80  23  11 0.00
Tue 09/01 07Z 0.04 2002  81  23  11 0.00
Tue 09/01 08Z 0.03 1903  82  24  12 0.00
Tue 09/01 09Z 0.02 1805  84  24  12 0.00
Tue 09/01 10Z 0.04 1905  86  26  12 0.00
Tue 09/01 11Z 0.03 1707  87  33  12 0.00

Run total areal avg QPF for the greens is: 0.47 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