NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260907_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)
=== ===== === ==== ==== === === === ====
Mon 09/07 00Z 0.26 3416  79  10   7 0.00
Mon 09/07 01Z 0.36 3317  78   9   7 0.00
Mon 09/07 02Z 0.40 3318  81  12   7 0.00
Mon 09/07 03Z 0.36 3319  84  16   8 0.00
Mon 09/07 04Z 0.37 3320  84  16   8 0.00
Mon 09/07 05Z 0.36 3320  83  17   8 0.00
Mon 09/07 06Z 0.28 3320  79  20   8 0.00
Mon 09/07 07Z 0.21 3419  77  24   8 0.00
Mon 09/07 08Z 0.22 3419  75  28   8 0.00
Mon 09/07 09Z 0.26 3320  74  32   8 0.00
Mon 09/07 10Z 0.30 3321  72  33   8 0.00
Mon 09/07 11Z 0.34 3323  67  30   8 0.00
Mon 09/07 12Z 0.36 3324  65  28   8 0.00
Mon 09/07 13Z 0.38 3325  65  21   8 0.00
Mon 09/07 14Z 0.31 3424  63  17   8 0.00
Mon 09/07 15Z 0.33 3424  64  12   8 0.00
Mon 09/07 16Z 0.60 3421  66  10   9 0.00
Mon 09/07 17Z 1.29 3418  67   8   9 0.00
Mon 09/07 18Z 2.62 3318  67   6   9 0.00
Mon 09/07 19Z 4.09 3318  69   5   9 0.00
Mon 09/07 20Z 2.78 3216  67   4   9 0.00
Mon 09/07 21Z 3.10 3216  70   4   9 0.00
Mon 09/07 22Z 1.78 3116  71   6   9 0.00
Mon 09/07 23Z 1.91 3118  73   9   9 0.00
Tue 09/08 00Z 1.59 3120  76  18   9 0.00
Tue 09/08 01Z 1.39 3121  80  32   9 0.00
Tue 09/08 02Z 1.08 3222  80  45   9 0.00
Tue 09/08 03Z 0.96 3222  80  53   9 0.00
Tue 09/08 04Z 0.90 3223  80  57   9 0.00
Tue 09/08 05Z 0.73 3223  80  57   9 0.00
Tue 09/08 06Z 0.60 3220  81  57   9 0.00
Tue 09/08 07Z 0.53 3219  82  63  10 0.00
Tue 09/08 08Z 0.51 3119  84  69  10 0.00
Tue 09/08 09Z 0.49 3118  86  76  10 0.00
Tue 09/08 10Z 0.51 3119  88  80  10 0.01
Tue 09/08 11Z 0.51 3120  91  78   9 0.02
Tue 09/08 12Z 0.48 3120  92  75   9 0.01
Tue 09/08 13Z 0.42 3119  92  70   9 0.00
Tue 09/08 14Z 0.37 3118  93  64   9 0.01
Tue 09/08 15Z 0.32 3217  89  68  10 0.00
Tue 09/08 16Z 0.30 3216  87  59  10 0.00
Tue 09/08 17Z 0.30 3215  84  64  10 0.00
Tue 09/08 18Z 0.28 3213  81  69  10 0.00
Tue 09/08 19Z 0.24 3212  75  64  10 0.00
Tue 09/08 20Z 0.21 3211  71  56  10 0.00
Tue 09/08 21Z 0.20 3209  68  69  10 0.00
Tue 09/08 22Z 0.21 3108  68  81  11 0.00
Tue 09/08 23Z 0.21 3007  69  73  11 0.00
Wed 09/09 00Z 0.24 2907  71  76  11 0.00
Wed 09/09 01Z 0.26 2807  75  73  11 0.00
Wed 09/09 02Z 0.26 2707  79  73  11 0.00
Wed 09/09 03Z 0.27 2607  85  65  11 0.00
Wed 09/09 04Z 0.25 2407  91  67  11 0.00
Wed 09/09 05Z 0.23 2308  94  70  11 0.00
Wed 09/09 06Z 0.23 2209  95  75  11 0.00
Wed 09/09 07Z 0.24 2211  95  75  11 0.00
Wed 09/09 08Z 0.29 2113  95  74  11 0.00
Wed 09/09 09Z 0.32 2116  94  70  11 0.00
Wed 09/09 10Z 0.44 2219  93  65  11 0.00
Wed 09/09 11Z 0.41 2219  86  60  11 0.00

Run total areal avg QPF for the greens is: 0.05 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