NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261011_1800
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 10/11 18Z 0.17 2013  69  92   9 0.00
Sun 10/11 19Z 0.17 2014  67  95   9 0.00
Sun 10/11 20Z 0.13 1917  58  96   9 0.00
Sun 10/11 21Z 0.13 1818  62  90   8 0.00
Sun 10/11 22Z 0.13 1818  76  92   8 0.00
Sun 10/11 23Z 0.16 1919  87  97   8 0.00
Mon 10/12 00Z 0.17 1821  94  96   7 0.01
Mon 10/12 01Z 0.17 1918  96  94   8 0.02
Mon 10/12 02Z 0.16 2013  97  96   9 0.04
Mon 10/12 03Z 0.14 2108  98  98   9 0.06
Mon 10/12 04Z 0.14 2606  97  93   9 0.06
Mon 10/12 05Z 0.11 2705  97  87   9 0.04
Mon 10/12 06Z 0.08 2804  97  86   9 0.03
Mon 10/12 07Z 0.08 3105  98  85   9 0.04
Mon 10/12 08Z 0.06 3308  97  81   9 0.03
Mon 10/12 09Z 0.04 3410  96  81   9 0.01
Mon 10/12 10Z 0.06 3312  98  82   9 0.00
Mon 10/12 11Z 0.06 3314  97  76   9 0.00
Mon 10/12 12Z 0.05 3415  93  56  10 0.00
Mon 10/12 13Z 0.05 3416  85  35  11 0.00
Mon 10/12 14Z 0.05 3416  75  25  12 0.00
Mon 10/12 15Z 0.06 3316  66  24  12 0.00
Mon 10/12 16Z 0.09 3315  64  32  13 0.00
Mon 10/12 17Z 0.14 3215  68  56  13 0.00
Mon 10/12 18Z 0.18 3115  71  65  13 0.00
Mon 10/12 19Z 0.24 3117  75  64  12 0.00
Mon 10/12 20Z 0.30 3017  82  66  11 0.00
Mon 10/12 21Z 0.33 3018  88  67  10 0.00
Mon 10/12 22Z 0.29 3117  89  69  10 0.00
Mon 10/12 23Z 0.27 3117  94  81   9 0.00
Tue 10/13 00Z 0.24 3116  95  84   9 0.01
Tue 10/13 01Z 0.17 3112  95  82   9 0.00
Tue 10/13 02Z 0.12 3210  97  92   8 0.01
Tue 10/13 03Z 0.09 3207  98  96   8 0.01
Tue 10/13 04Z 0.08 3205  98  98   7 0.01
Tue 10/13 05Z 0.04 3102  98  92   8 0.01
Tue 10/13 06Z 0.03 1602  98  99   7 0.00
Tue 10/13 07Z 0.08 1507  99  98   7 0.06
Tue 10/13 08Z 0.06 1611  99  96   7 0.05
Tue 10/13 09Z 0.07 1615  99  96   6 0.04
Tue 10/13 10Z 0.06 1618  97  98   7 0.03
Tue 10/13 11Z 0.04 1718  96  98   7 0.02
Tue 10/13 12Z 0.06 1719  97  95   8 0.04
Tue 10/13 13Z 0.09 1821  97  95   8 0.04
Tue 10/13 14Z 0.12 1822  97  91   8 0.03
Tue 10/13 15Z 0.15 1826  98  93   9 0.02
Tue 10/13 16Z 0.18 1927  98  87  10 0.02
Tue 10/13 17Z 0.21 1928  98  76  11 0.02
Tue 10/13 18Z 0.24 1929  97  42  12 0.02
Tue 10/13 19Z 0.27 2030  96  92  12 0.02
Tue 10/13 20Z 0.33 2032  88  75  13 0.01
Tue 10/13 21Z 0.43 2134  90  73  13 0.00
Tue 10/13 22Z 0.51 2235  91  84  14 0.00
Tue 10/13 23Z 0.58 2236  94  67  14 0.00
Wed 10/14 00Z 0.68 2337  96  58  13 0.02
Wed 10/14 01Z 0.75 2436  98  58  13 0.04
Wed 10/14 02Z 0.80 2436  98  45  13 0.04
Wed 10/14 03Z 0.83 2435  97  52  13 0.03
Wed 10/14 04Z 0.89 2536  97  51  13 0.04
Wed 10/14 05Z 0.95 2537  97  51  13 0.03

Run total areal avg QPF for the Central_Greens is: 1.01 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