NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260905_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)
=== ===== === ==== ==== === === === ====
Sat 09/05 12Z 0.11 0016  97  82   9 0.00
Sat 09/05 13Z 0.21 0115  97  79   8 0.00
Sat 09/05 14Z 0.18 0013  97  79   8 0.00
Sat 09/05 15Z 0.16 0011  97  78   8 0.00
Sat 09/05 16Z 0.15 0010  97  77   9 0.01
Sat 09/05 17Z 0.16 0010  96  74   9 0.01
Sat 09/05 18Z 0.17 0010  95  72   9 0.01
Sat 09/05 19Z 0.22 0110  94  70   9 0.01
Sat 09/05 20Z 0.21 0109  94  70   9 0.00
Sat 09/05 21Z 0.20 0109  94  71   9 0.00
Sat 09/05 22Z 0.20 0110  95  74   9 0.00
Sat 09/05 23Z 0.21 0111  96  76   9 0.01
Sun 09/06 00Z 0.28 0212  96  77   9 0.01
Sun 09/06 01Z 0.40 0413  96  84   9 0.02
Sun 09/06 02Z 0.44 0612  96  88   8 0.02
Sun 09/06 03Z 0.41 0811  96  90   8 0.01
Sun 09/06 04Z 0.41 1011  96  93   7 0.01
Sun 09/06 05Z 0.33 1110  94  95   7 0.01
Sun 09/06 06Z 0.26 1108  94  96   7 0.01
Sun 09/06 07Z 0.22 1006  95  97   7 0.02
Sun 09/06 08Z 0.16 0904  96  98   6 0.05
Sun 09/06 09Z 0.15 0504  96  94   6 0.05
Sun 09/06 10Z 0.15 0306  94  93   6 0.03
Sun 09/06 11Z 0.14 0108  93  83   6 0.01
Sun 09/06 12Z 0.15 0111  89  77   6 0.00
Sun 09/06 13Z 0.15 0011  85  72   6 0.00
Sun 09/06 14Z 0.19 0012  85  68   6 0.00
Sun 09/06 15Z 0.31 0012  87  62   6 0.00
Sun 09/06 16Z 0.38 0011  88  55   6 0.00
Sun 09/06 17Z 0.43 3511  88  52   7 0.00
Sun 09/06 18Z 0.22 3511  86  49   7 0.00
Sun 09/06 19Z 0.13 3511  86  40   7 0.00
Sun 09/06 20Z 0.19 3412  87  31   7 0.00
Sun 09/06 21Z 0.15 3413  87  17   7 0.00
Sun 09/06 22Z 0.07 3414  82  10   7 0.00
Sun 09/06 23Z 0.04 3515  74  30   8 0.00
Mon 09/07 00Z 0.06 3418  71  53   7 0.00
Mon 09/07 01Z 0.08 3418  79  63   7 0.00
Mon 09/07 02Z 0.14 3319  86  59   7 0.01
Mon 09/07 03Z 0.15 3319  92  44   7 0.02
Mon 09/07 04Z 0.12 3419  95  28   7 0.01
Mon 09/07 05Z 0.04 3419  93   7   7 0.01
Mon 09/07 06Z 0.03 3518  88   7   7 0.01
Mon 09/07 07Z 0.02 3419  84   6   7 0.00
Mon 09/07 08Z 0.03 3519  80   7   7 0.00
Mon 09/07 09Z 0.03 3419  77   7   7 0.00
Mon 09/07 10Z 0.09 3419  77   6   6 0.00
Mon 09/07 11Z 0.16 3319  79   6   6 0.00
Mon 09/07 12Z 0.20 3320  81   6   6 0.00
Mon 09/07 13Z 0.24 3320  83   5   6 0.00
Mon 09/07 14Z 0.28 3220  84   7   6 0.00
Mon 09/07 15Z 0.31 3320  84   6   6 0.00
Mon 09/07 16Z 0.82 3318  84   5   6 0.00
Mon 09/07 17Z 1.30 3218  85   5   6 0.00
Mon 09/07 18Z 1.63 3116  89   8   7 0.00
Mon 09/07 19Z 0.85 3115  90  13   7 0.00
Mon 09/07 20Z 0.62 3116  87  20   8 0.00
Mon 09/07 21Z 0.67 3018  86  39   8 0.00
Mon 09/07 22Z 0.66 3019  85  65   8 0.00
Mon 09/07 23Z 0.53 3120  81  64   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.36 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