NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260331_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)
=== ===== === ==== ==== === === === ====
Tue 03/31 18Z 0.72 2422  97  87   7 0.00
Tue 03/31 19Z 0.67 2421  95  90   7 0.02
Tue 03/31 20Z 0.67 2323  98  83   8 0.03
Tue 03/31 21Z 0.70 2423  96  67   8 0.01
Tue 03/31 22Z 0.69 2423  95  55   9 0.01
Tue 03/31 23Z 0.56 2221  97  86   9 0.07
Wed 04/01 00Z 0.46 2024  98  98   9 0.26
Wed 04/01 01Z 0.64 2224  94  93   9 0.48
Wed 04/01 02Z 0.46 2119  94  95  10 0.25
Wed 04/01 03Z 0.47 2320  95  96  10 0.25
Wed 04/01 04Z 0.67 2231  98  89  10 0.17
Wed 04/01 05Z 1.08 2339  98  86  10 0.17
Wed 04/01 06Z 1.35 2438  98  94   9 0.18
Wed 04/01 07Z 1.16 2535  99  84   9 0.06
Wed 04/01 10Z 0.66 2730  99  48   7 0.04
Wed 04/01 11Z 0.47 2827  97  47   6 0.03
Wed 04/01 12Z 0.35 2924  95  36   5 0.03
Wed 04/01 13Z 0.30 3023  91  32   5 0.02
Wed 04/01 14Z 0.23 3122  84  23   5 0.02
Wed 04/01 15Z 0.19 3121  77  20   4 0.01
Wed 04/01 16Z 0.18 3220  73  16   3 0.01
Wed 04/01 17Z 0.18 3219  72  15   2 0.00
Wed 04/01 18Z 0.16 3217  70  14   1 0.00
Wed 04/01 20Z 0.12 3315  67  16   0 0.00
Wed 04/01 21Z 0.06 3413  64  19   0 0.00
Wed 04/01 22Z 0.03 3412  61  22   0 0.00
Wed 04/01 23Z 0.03 3411  59  25   0 0.00
Thu 04/02 00Z 0.02 3510  56  26   0 0.00
Thu 04/02 01Z 0.05 0009  52  26   0 0.00
Thu 04/02 02Z 0.09 0307  46  30   0 0.00
Thu 04/02 03Z 0.09 0505  46  32   0 0.00
Thu 04/02 04Z 0.11 0805  45  35   0 0.00
Thu 04/02 05Z 0.12 1107  46  40   0 0.00
Thu 04/02 06Z 0.09 1409  53  42   0 0.00
Thu 04/02 07Z 0.07 1511  61  45   0 0.00
Thu 04/02 08Z 0.06 1512  69  50   0 0.00
Thu 04/02 09Z 0.05 1610  70  56   0 0.00
Thu 04/02 10Z 0.07 1511  71  85   0 0.00
Thu 04/02 11Z 0.08 1513  69  94   1 0.00
Thu 04/02 12Z 0.08 1513  70  98   1 0.00
Thu 04/02 13Z 0.10 1412  75  99   1 0.00
Thu 04/02 14Z 0.12 1313  80  98   1 0.00
Thu 04/02 15Z 0.13 1314  84  97   1 0.01
Thu 04/02 16Z 0.11 1414  91  99   0 0.01
Thu 04/02 17Z 0.13 1415  95  99   0 0.01
Thu 04/02 18Z 0.13 1415  96  99   0 0.01
Thu 04/02 19Z 0.13 1416  96  98   0 0.02
Thu 04/02 20Z 0.10 1515  96  99   0 0.03
Thu 04/02 21Z 0.07 1516  96  98   1 0.02
Thu 04/02 22Z 0.04 1617  96  98   2 0.02
Thu 04/02 23Z 0.02 1619  96  96   2 0.02
Fri 04/03 00Z 0.05 1721  97  94   3 0.02
Fri 04/03 01Z 0.10 1822  97  81   4 0.02
Fri 04/03 04Z 0.19 2024  97  57   8 0.02
Fri 04/03 05Z 0.21 2025  95  44   9 0.02

Run total areal avg QPF for the Central_Greens is: 2.35 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