NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260906_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 09/06 12Z 0.09 0010  91  83   7 0.00
Sun 09/06 13Z 0.14 0112  90  80   7 0.00
Sun 09/06 14Z 0.15 0112  91  78   7 0.00
Sun 09/06 15Z 0.15 0112  91  64   7 0.00
Sun 09/06 16Z 0.16 0112  91  55   7 0.00
Sun 09/06 17Z 0.15 0012  90  52   6 0.00
Sun 09/06 18Z 0.14 0012  89  53   6 0.00
Sun 09/06 19Z 0.10 3513  86  41   7 0.00
Sun 09/06 20Z 0.13 3514  83  22   7 0.00
Sun 09/06 21Z 0.13 3415  83   7   7 0.00
Sun 09/06 22Z 0.06 3417  83   5   7 0.01
Sun 09/06 23Z 0.07 3519  86   8   7 0.00
Mon 09/07 00Z 0.05 3521  85   6   7 0.00
Mon 09/07 01Z 0.08 3522  86   8   7 0.00
Mon 09/07 02Z 0.10 3522  84  11   7 0.00
Mon 09/07 03Z 0.06 3522  83  13   7 0.00
Mon 09/07 04Z 0.06 3422  86  13   7 0.00
Mon 09/07 05Z 0.08 3421  88  16   6 0.00
Mon 09/07 06Z 0.14 3421  89  10   6 0.00
Mon 09/07 07Z 0.20 3321  87  10   6 0.00
Mon 09/07 08Z 0.21 3322  85  12   6 0.00
Mon 09/07 09Z 0.17 3322  78  16   7 0.00
Mon 09/07 10Z 0.14 3422  73  20   7 0.00
Mon 09/07 11Z 0.06 3422  66  23   7 0.00
Mon 09/07 12Z 0.06 3422  63  24   7 0.00
Mon 09/07 13Z 0.09 3422  64  23   7 0.00
Mon 09/07 14Z 0.13 3422  68  21   7 0.00
Mon 09/07 15Z 0.20 3320  71  16   7 0.00
Mon 09/07 16Z 0.63 3319  73  10   7 0.00
Mon 09/07 17Z 1.95 3317  75   8   7 0.00
Mon 09/07 18Z 2.89 3316  74   8   8 0.00
Mon 09/07 19Z 2.56 3316  71   8   8 0.00
Mon 09/07 20Z 2.33 3316  71   6   8 0.00
Mon 09/07 21Z 1.70 3215  72   4   8 0.00
Mon 09/07 22Z 0.85 3216  74   4   8 0.00
Mon 09/07 23Z 0.75 3218  75   5   8 0.00
Tue 09/08 00Z 1.02 3120  77   7   8 0.00
Tue 09/08 01Z 0.75 3121  82  13   8 0.00
Tue 09/08 02Z 0.38 3219  80  22   8 0.00
Tue 09/08 03Z 0.33 3222  82  34   9 0.00
Tue 09/08 04Z 0.29 3222  83  48   9 0.00
Tue 09/08 05Z 0.28 3221  83  66   9 0.00
Tue 09/08 06Z 0.30 3221  85  72   9 0.00
Tue 09/08 07Z 0.31 3221  85  72   9 0.00
Tue 09/08 08Z 0.31 3220  88  60   9 0.00
Tue 09/08 09Z 0.36 3122  93  57   9 0.01
Tue 09/08 10Z 0.36 3224  95  47   9 0.01
Tue 09/08 11Z 0.32 3224  93  27   9 0.01
Tue 09/08 12Z 0.31 3224  90   8   9 0.01
Tue 09/08 13Z 0.27 3223  85   3   9 0.01
Tue 09/08 14Z 0.23 3223  78   4   9 0.01
Tue 09/08 15Z 0.16 3321  69   4   9 0.00
Tue 09/08 16Z 0.15 3320  65   4   9 0.00
Tue 09/08 17Z 0.14 3318  60   4   9 0.00
Tue 09/08 18Z 0.08 3315  54   5   9 0.00
Tue 09/08 19Z 0.09 3314  52   7   9 0.00
Tue 09/08 20Z 0.07 3313  45   8  10 0.00
Tue 09/08 21Z 0.03 3411  40   6  10 0.00
Tue 09/08 22Z 0.04 3409  37   6  10 0.00
Tue 09/08 23Z 0.02 3408  30   4  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.07 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