NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260514_0000
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)
=== ===== === ==== ==== === === === ====
Thu 05/14 00Z 0.26 1826  85  64   5 0.00
Thu 05/14 01Z 0.25 1828  76  54   6 0.00
Thu 05/14 02Z 0.26 1928  75  53   6 0.00
Thu 05/14 03Z 0.22 1827  75  54   6 0.00
Thu 05/14 04Z 0.19 1825  73  59   7 0.00
Thu 05/14 05Z 0.21 1826  75  75   7 0.00
Thu 05/14 06Z 0.25 1927  80  84   6 0.00
Thu 05/14 07Z 0.21 1924  88  81   6 0.00
Thu 05/14 08Z 0.14 1824  94  85   5 0.02
Thu 05/14 09Z 0.07 1724  98  90   5 0.06
Thu 05/14 10Z 0.07 1725  98  91   5 0.03
Thu 05/14 11Z 0.10 1725  98  96   5 0.04
Thu 05/14 12Z 0.17 1823  98  98   5 0.06
Thu 05/14 13Z 0.17 1819  99  92   5 0.04
Thu 05/14 14Z 0.09 1715  99  89   5 0.03
Thu 05/14 15Z 0.10 1614  99  91   5 0.06
Thu 05/14 16Z 0.20 1415  99  99   5 0.14
Thu 05/14 17Z 0.32 1318  99  99   5 0.22
Thu 05/14 18Z 0.40 1217  99  99   5 0.21
Thu 05/14 19Z 0.48 1220  99  98   5 0.20
Thu 05/14 20Z 0.53 1118  99  98   5 0.16
Thu 05/14 21Z 0.46 1114  99  97   5 0.14
Thu 05/14 22Z 0.49 1114  99  98   5 0.13
Thu 05/14 23Z 0.48 0913  99  97   5 0.12
Fri 05/15 00Z 0.42 0911  97  97   4 0.11
Fri 05/15 01Z 0.50 0913  98  97   4 0.10
Fri 05/15 02Z 0.48 0914  96  96   4 0.10
Fri 05/15 03Z 0.60 0817  96  96   3 0.13
Fri 05/15 04Z 0.72 0923  97  97   3 0.10
Fri 05/15 05Z 0.82 1029  97  95   4 0.07
Fri 05/15 06Z 0.84 1030  94  94   3 0.05
Fri 05/15 07Z 0.84 1031  96  89   3 0.04
Fri 05/15 08Z 0.83 1029  95  92   3 0.03
Fri 05/15 09Z 0.82 1028  96  94   3 0.02
Fri 05/15 10Z 0.80 1026  94  96   2 0.02
Fri 05/15 11Z 0.80 0924  93  96   2 0.03
Fri 05/15 12Z 0.78 0923  91  95   2 0.01
Fri 05/15 13Z 0.83 0822  89  94   2 0.01
Fri 05/15 14Z 0.87 0822  88  92   2 0.01
Fri 05/15 15Z 0.89 0919  91  88   2 0.00
Fri 05/15 16Z 1.02 0815  95  86   2 0.00
Fri 05/15 17Z 0.89 0812  95  87   2 0.01
Fri 05/15 18Z 0.91 0911  95  87   3 0.01
Fri 05/15 19Z 0.67 0909  93  89   3 0.01
Fri 05/15 20Z 0.54 0908  90  90   3 0.00
Fri 05/15 21Z 0.34 1006  88  90   3 0.00
Fri 05/15 22Z 0.21 1104  87  92   3 0.00
Fri 05/15 23Z 0.18 1102  86  88   4 0.00
Sat 05/16 00Z 0.13 1201  84  80   4 0.00
Sat 05/16 01Z 0.11 3000  80  72   4 0.00
Sat 05/16 02Z 0.11 2901  76  60   4 0.00
Sat 05/16 03Z 0.10 2501  73  54   5 0.00
Sat 05/16 04Z 0.18 2306  79  51   4 0.00
Sat 05/16 05Z 0.25 2408  81  47   4 0.00
Sat 05/16 06Z 0.27 2508  80  42   4 0.00
Sat 05/16 07Z 0.33 2510  85  40   4 0.00
Sat 05/16 08Z 0.37 2512  87  37   4 0.00
Sat 05/16 09Z 0.37 2513  85  34   4 0.00
Sat 05/16 10Z 0.46 2516  85  38   4 0.00
Sat 05/16 11Z 0.50 2517  83  37   4 0.00

Run total areal avg QPF for the Central_Greens is: 2.52 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