NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260429_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)
=== ===== === ==== ==== === === === ====
Wed 04/29 06Z 0.29 2018  65  75   3 0.00
Wed 04/29 07Z 0.30 2019  65  90   4 0.00
Wed 04/29 08Z 0.28 2018  66  95   4 0.00
Wed 04/29 09Z 0.25 2016  68  86   4 0.00
Wed 04/29 12Z 0.25 2015  78  59   5 0.00
Wed 04/29 13Z 0.17 2012  76  51   6 0.00
Wed 04/29 14Z 0.10 1909  75  47   6 0.00
Wed 04/29 15Z 0.03 1708  74  47   6 0.00
Wed 04/29 16Z 0.24 1510  73  27   6 0.00
Wed 04/29 17Z 0.25 1611  73  39   5 0.00
Wed 04/29 18Z 0.83 1612  72  62   5 0.00
Wed 04/29 19Z 1.87 1514  71  58   5 0.00
Wed 04/29 20Z 2.41 1514  73  51   5 0.00
Wed 04/29 21Z 2.12 1517  75  50   5 0.00
Wed 04/29 22Z 0.48 1517  76  57   5 0.00
Wed 04/29 23Z 0.16 1618  80  67   5 0.00
Thu 04/30 00Z 0.08 1619  87  81   5 0.00
Thu 04/30 01Z 0.05 1621  90  85   6 0.00
Thu 04/30 02Z 0.04 1622  89  91   6 0.00
Thu 04/30 03Z 0.05 1623  85  92   6 0.00
Thu 04/30 04Z 0.06 1625  82  96   6 0.00
Thu 04/30 05Z 0.05 1627  81  96   6 0.00
Thu 04/30 06Z 0.05 1628  88  96   4 0.01
Thu 04/30 07Z 0.06 1628  91  97   4 0.01
Thu 04/30 08Z 0.05 1628  95  99   4 0.03
Thu 04/30 09Z 0.04 1629  96  97   4 0.03
Thu 04/30 10Z 0.04 1728  95  98   3 0.06
Thu 04/30 11Z 0.05 1727  95  98   4 0.11
Thu 04/30 12Z 0.12 1724  98  99   2 0.09
Thu 04/30 13Z 0.14 1821  98  99   2 0.09
Thu 04/30 14Z 0.22 1920  95  99   2 0.07
Thu 04/30 15Z 0.25 1917  97  96   2 0.05
Thu 04/30 16Z 0.26 2012  98  91   1 0.04
Thu 04/30 17Z 0.26 2207  99  88   1 0.02
Thu 04/30 18Z 0.22 2405  99  73   1 0.02
Thu 04/30 19Z 0.25 2705  99  74   1 0.01
Thu 04/30 20Z 0.25 2906  99  85   1 0.01
Thu 04/30 21Z 0.26 3108  99  87   1 0.01
Thu 04/30 22Z 0.24 3211  98  85   1 0.01
Thu 04/30 23Z 0.25 3215  98  83   0 0.01
Fri 05/01 00Z 0.20 3318  97  77   0 0.01
Fri 05/01 01Z 0.30 3219  97  65   0 0.01
Fri 05/01 02Z 0.36 3219  96  64   0 0.01
Fri 05/01 03Z 0.39 3220  96  63  -1 0.01
Fri 05/01 04Z 0.40 3221  94  63  -1 0.01
Fri 05/01 05Z 0.41 3121  93  62  -2 0.01
Fri 05/01 06Z 0.42 3122  95  51  -2 0.01
Fri 05/01 07Z 0.46 3121  96  49  -3 0.01
Fri 05/01 08Z 0.48 3121  95  53  -3 0.01
Fri 05/01 09Z 0.45 3121  90  41  -3 0.01
Fri 05/01 10Z 0.44 3122  89  36  -3 0.01
Fri 05/01 11Z 0.44 3021  88  34  -3 0.01
Fri 05/01 12Z 0.48 3020  88  36  -4 0.00
Fri 05/01 13Z 0.51 3018  88  35  -4 0.00
Fri 05/01 14Z 0.72 3016  87  25  -4 0.00
Fri 05/01 15Z 2.12 2914  91  21  -4 0.00
Fri 05/01 16Z 2.64 2812  92  20  -4 0.00
Fri 05/01 17Z 3.67 2811  91  23  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.80 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