NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260927_0600
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 09/27 06Z 0.85 0629  85  89   9 0.00
Sun 09/27 07Z 0.89 0633  80  88   9 0.00
Sun 09/27 08Z 0.89 0634  79  89   9 0.00
Sun 09/27 09Z 0.87 0636  82  92   9 0.01
Sun 09/27 10Z 0.82 0637  90  86  10 0.02
Sun 09/27 11Z 0.80 0738  95  85  10 0.03
Sun 09/27 12Z 0.79 0738  96  84  10 0.03
Sun 09/27 13Z 0.73 0837  96  79  10 0.04
Sun 09/27 14Z 0.68 0835  96  77  11 0.03
Sun 09/27 15Z 0.63 0833  96  77  11 0.02
Sun 09/27 16Z 0.61 0832  96  83  11 0.04
Sun 09/27 17Z 0.62 0832  97  88  11 0.04
Sun 09/27 18Z 0.60 0830  96  91  11 0.05
Sun 09/27 19Z 0.60 0831  97  92  11 0.05
Sun 09/27 20Z 0.61 0830  96  79  11 0.02
Sun 09/27 21Z 0.62 0830  96  47  11 0.02
Sun 09/27 22Z 0.62 0931  96  19  11 0.02
Sun 09/27 23Z 0.64 0932  96  39  11 0.02
Mon 09/28 00Z 0.62 0932  95  58  11 0.02
Mon 09/28 01Z 0.60 0932  96  61  11 0.02
Mon 09/28 02Z 0.59 0932  96  67  11 0.02
Mon 09/28 03Z 0.58 0932  95  68  11 0.02
Mon 09/28 04Z 0.57 0932  95  74  12 0.01
Mon 09/28 05Z 0.56 0932  95  67  12 0.01
Mon 09/28 06Z 0.55 0931  95  70  12 0.01
Mon 09/28 07Z 0.53 0930  95  86  12 0.03
Mon 09/28 08Z 0.50 1029  95  86  12 0.02
Mon 09/28 09Z 0.47 1027  94  81  12 0.02
Mon 09/28 10Z 0.43 1025  94  81  12 0.01
Mon 09/28 11Z 0.40 0922  95  78  12 0.02
Mon 09/28 12Z 0.40 0922  96  86  12 0.02
Mon 09/28 13Z 0.39 0821  96  86  12 0.01
Mon 09/28 14Z 0.42 0821  97  93  11 0.06
Mon 09/28 15Z 0.42 0821  98  92  10 0.13
Mon 09/28 16Z 0.44 0820  98  92   9 0.20
Mon 09/28 17Z 0.41 0818  98  87   9 0.08
Mon 09/28 18Z 0.36 0817  98  89   9 0.04
Mon 09/28 19Z 0.35 0816  98  81  10 0.03
Mon 09/28 20Z 0.33 0715  98  76  10 0.02
Mon 09/28 21Z 0.30 0714  98  88  10 0.01
Mon 09/28 22Z 0.28 0614  97  89  10 0.02
Mon 09/28 23Z 0.27 0513  97  93  10 0.02
Tue 09/29 00Z 0.25 0512  97  88   9 0.03
Tue 09/29 01Z 0.23 0511  97  92   9 0.03
Tue 09/29 02Z 0.22 0610  97  95   9 0.04
Tue 09/29 03Z 0.19 0609  97  97   9 0.04
Tue 09/29 04Z 0.14 0506  97  97   8 0.02
Tue 09/29 05Z 0.09 0305  98  98   8 0.02
Tue 09/29 06Z 0.08 0206  98  96   9 0.02
Tue 09/29 07Z 0.07 0107  98  94   9 0.01
Tue 09/29 08Z 0.06 0108  98  94   9 0.00
Tue 09/29 09Z 0.06 0010  99  93   9 0.00
Tue 09/29 10Z 0.08 0110  98  91   9 0.00
Tue 09/29 11Z 0.09 0110  96  88   9 0.00
Tue 09/29 12Z 0.09 0109  97  87   9 0.00
Tue 09/29 13Z 0.06 0009  98  87   9 0.00
Tue 09/29 14Z 0.04 0009  98  87   9 0.00
Tue 09/29 15Z 0.04 3510  99  88   9 0.01
Tue 09/29 16Z 0.05 3511  98  88   9 0.01
Tue 09/29 17Z 0.05 0010  97  88   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.52 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