NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260704_0600
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)
=== ===== === ==== ==== === === === ====
Sat 07/04 06Z 0.72 2920  80  78  17 0.00
Sat 07/04 07Z 0.81 2923  80  69  16 0.00
Sat 07/04 08Z 0.86 3024  84  73  16 0.00
Sat 07/04 09Z 0.76 3023  85  69  16 0.00
Sat 07/04 10Z 0.65 3022  85  66  16 0.00
Sat 07/04 11Z 0.51 3120  83  61  16 0.00
Sat 07/04 12Z 0.44 3117  82  61  16 0.00
Sat 07/04 13Z 0.45 3016  84  64  15 0.00
Sat 07/04 14Z 0.52 3015  85  74  15 0.00
Sat 07/04 15Z 0.64 2916  87  82  15 0.00
Sat 07/04 16Z 0.71 2916  90  83  14 0.00
Sat 07/04 17Z 0.70 2915  91  74  14 0.07
Sat 07/04 18Z 0.89 3015  89  64  14 0.02
Sat 07/04 19Z 1.00 3114  86  52  14 0.00
Sat 07/04 20Z 1.55 3114  83  46  14 0.00
Sat 07/04 21Z 1.57 3214  81  38  14 0.05
Sat 07/04 22Z 1.08 3214  80  31  14 0.00
Sat 07/04 23Z 0.54 3314  79  26  13 0.00
Sun 07/05 00Z 0.37 3314  75  22  13 0.00
Sun 07/05 01Z 0.25 3415  74  18  13 0.00
Sun 07/05 02Z 0.17 3413  72  19  13 0.00
Sun 07/05 03Z 0.10 3513  72  16  13 0.00
Sun 07/05 04Z 0.05 3513  72  12  12 0.00
Sun 07/05 05Z 0.05 0011  72  14  12 0.00
Sun 07/05 06Z 0.05 0010  72  17  12 0.00
Sun 07/05 07Z 0.11 0109  71  14  12 0.00
Sun 07/05 08Z 0.12 0108  71  13  12 0.00
Sun 07/05 09Z 0.11 0107  71  16  11 0.00
Sun 07/05 10Z 0.12 0207  71  12  11 0.00
Sun 07/05 11Z 0.14 0206  70  11  11 0.00
Sun 07/05 12Z 0.13 0206  70   8  11 0.00
Sun 07/05 13Z 0.17 0304  72   7  11 0.00
Sun 07/05 14Z 0.44 0203  75   7  11 0.00
Sun 07/05 15Z 0.61 0201  76   7  11 0.00
Sun 07/05 16Z 0.55 3501  77   8  11 0.00
Sun 07/05 17Z 0.27 3401  79  11  11 0.01
Sun 07/05 18Z 0.31 3302  81  10  11 0.00
Sun 07/05 19Z 0.19 3402  81   7  12 0.00
Sun 07/05 20Z 0.19 3503  81   6  12 0.00
Sun 07/05 21Z 0.13 3503  80   7  12 0.00
Sun 07/05 22Z 0.15 0104  79   6  12 0.00
Sun 07/05 23Z 0.23 0204  79   6  12 0.00
Mon 07/06 00Z 0.38 0405  79   4  12 0.00
Mon 07/06 01Z 0.55 0606  78   4  12 0.00
Mon 07/06 02Z 0.64 0707  78   4  11 0.00
Mon 07/06 03Z 0.67 0808  79   4  11 0.00
Mon 07/06 04Z 0.71 0809  79   4  11 0.00
Mon 07/06 05Z 0.60 1008  78   4  11 0.00
Mon 07/06 06Z 0.49 1108  80   4  11 0.00
Mon 07/06 07Z 0.37 1309  81   4  11 0.00
Mon 07/06 08Z 0.29 1409  82   5  11 0.00
Mon 07/06 09Z 0.22 1510  83   5  11 0.00
Mon 07/06 10Z 0.17 1611  84   5  11 0.00
Mon 07/06 11Z 0.14 1611  86   5  11 0.00
Mon 07/06 12Z 0.14 1610  84   5  11 0.00
Mon 07/06 13Z 0.17 1609  84   5  10 0.00
Mon 07/06 14Z 0.20 1608  84   5  10 0.00
Mon 07/06 15Z 0.41 1408  84   6  10 0.00
Mon 07/06 16Z 0.84 1406  84   6  11 0.00
Mon 07/06 17Z 1.40 1407  84   6  11 0.00

Run total areal avg QPF for the greens is: 0.15 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