NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260504_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)
=== ===== === ==== ==== === === === ====
Mon 05/04 12Z 0.83 2524  72  88   2 0.00
Mon 05/04 13Z 1.03 2526  72  90   2 0.00
Mon 05/04 14Z 1.49 2427  72  89   2 0.00
Mon 05/04 15Z 3.36 2426  74  94   2 0.00
Mon 05/04 16Z 11.84 2422  76  85   2 0.00
Mon 05/04 17Z 15.24 2423  75  93   3 0.00
Mon 05/04 18Z 15.15 2424  73  88   4 0.00
Mon 05/04 19Z 14.59 2423  70  74   5 0.00
Mon 05/04 20Z 13.59 2422  67  65   5 0.00
Mon 05/04 21Z 11.25 2322  68  53   6 0.00
Mon 05/04 22Z 6.37 2322  67  48   6 0.00
Mon 05/04 23Z 2.17 2323  66  70   6 0.00
Tue 05/05 00Z 1.64 2325  67  61   6 0.00
Tue 05/05 01Z 1.17 2325  68  47   7 0.00
Tue 05/05 02Z 1.00 2325  68  18   7 0.00
Tue 05/05 03Z 1.02 2228  70  13   7 0.00
Tue 05/05 04Z 1.21 2233  75  16   6 0.00
Tue 05/05 05Z 1.14 2234  74  27   7 0.00
Tue 05/05 06Z 1.08 2236  71  15   7 0.00
Tue 05/05 07Z 0.94 2235  66  15   8 0.00
Tue 05/05 08Z 0.87 2234  66   9   8 0.00
Tue 05/05 09Z 0.80 2233  72  24   8 0.00
Tue 05/05 10Z 0.87 2232  78  45   8 0.00
Tue 05/05 11Z 0.82 2232  88  62   7 0.00
Tue 05/05 12Z 0.82 2233  90  66   7 0.00
Tue 05/05 13Z 1.06 2331  90  76   7 0.00
Tue 05/05 14Z 1.09 2329  87  76   8 0.00
Tue 05/05 15Z 2.15 2226  86  62   8 0.00
Tue 05/05 16Z 7.72 2227  84  69   8 0.00
Tue 05/05 17Z 10.20 2225  82  75   9 0.00
Tue 05/05 18Z 11.14 2125  79  65  10 0.00
Tue 05/05 19Z 8.13 2126  80  91  10 0.00
Tue 05/05 20Z 5.87 2128  81  84  10 0.02
Tue 05/05 21Z 2.63 2229  85  90  11 0.07
Tue 05/05 22Z 1.57 2328  85  85  11 0.32
Tue 05/05 23Z 0.99 2130  83  93  11 0.02
Wed 05/06 00Z 1.10 2531  95  96   9 0.49
Wed 05/06 01Z 0.95 2628  94  90   9 0.11
Wed 05/06 02Z 1.04 2624  99  94   7 0.13
Wed 05/06 03Z 0.59 2622  95  84   7 0.16
Wed 05/06 04Z 0.56 2622  92  93   6 0.05
Wed 05/06 05Z 0.54 2621  89  93   5 0.03
Wed 05/06 06Z 0.48 2620  83  91   5 0.03
Wed 05/06 07Z 0.42 2618  92  96   4 0.04
Wed 05/06 08Z 0.37 2518  92  90   5 0.04
Wed 05/06 09Z 0.31 2416  87  85   6 0.02
Wed 05/06 10Z 0.30 2415  81  69   6 0.00
Wed 05/06 11Z 0.26 2315  80  88   6 0.00
Wed 05/06 12Z 0.26 2214  85  96   6 0.00
Wed 05/06 13Z 0.18 2114  91  98   6 0.02
Wed 05/06 14Z 0.17 2015  94  83   7 0.02
Wed 05/06 15Z 0.16 1916  97  71   8 0.02
Wed 05/06 16Z 0.14 1918  97  67   8 0.00
Wed 05/06 17Z 0.12 1819  97  79   8 0.01
Wed 05/06 18Z 0.08 1721  97  97   8 0.03
Wed 05/06 19Z 0.11 1724  98  98   8 0.08
Wed 05/06 20Z 0.16 1727  97  99   7 0.13
Wed 05/06 21Z 0.21 1729  97  99   5 0.15
Wed 05/06 22Z 0.12 1730  96  99   5 0.15
Wed 05/06 23Z 0.10 1730  98  98   5 0.12

Run total areal avg QPF for the Central_Greens is: 2.26 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