NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260401_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 04/01 06Z 0.74 2329  97  98   9 0.00
Wed 04/01 07Z 0.79 2430  98  94   9 0.09
Wed 04/01 08Z 0.74 2629  98  96   8 0.12
Wed 04/01 09Z 0.66 2728  98  85   8 0.05
Wed 04/01 10Z 0.55 2826  98  88   7 0.02
Wed 04/01 11Z 0.44 2924  97  68   7 0.01
Wed 04/01 12Z 0.38 2923  95  70   7 0.01
Wed 04/01 13Z 0.33 2921  95  74   6 0.00
Wed 04/01 14Z 0.28 3020  97  63   5 0.01
Wed 04/01 15Z 0.25 3020  95  41   4 0.01
Wed 04/01 16Z 0.23 3018  89  34   3 0.00
Wed 04/01 17Z 0.23 3016  82  28   3 0.00
Wed 04/01 18Z 0.22 3015  74  20   2 0.00
Wed 04/01 19Z 0.19 3114  69  17   1 0.00
Wed 04/01 20Z 0.16 3112  64  17   0 0.00
Wed 04/01 21Z 0.12 3211  59  18   0 0.00
Wed 04/01 22Z 0.09 3211  55  19   1 0.00
Wed 04/01 23Z 0.05 3310  53  30   1 0.00
Thu 04/02 00Z 0.04 3507  52  30   1 0.00
Thu 04/02 01Z 0.04 3505  53  29   1 0.00
Thu 04/02 02Z 0.04 0104  50  31   1 0.00
Thu 04/02 03Z 0.05 0402  48  31   1 0.00
Thu 04/02 04Z 0.07 1003  48  37   1 0.00
Thu 04/02 05Z 0.09 1106  50  48   1 0.00
Thu 04/02 06Z 0.09 1308  59  51   0 0.00
Thu 04/02 07Z 0.11 1412  71  52   0 0.00
Thu 04/02 08Z 0.10 1412  81  46   0 0.01
Thu 04/02 09Z 0.09 1411  85  44   1 0.00
Thu 04/02 10Z 0.12 1312  89  44   1 0.01
Thu 04/02 11Z 0.13 1313  92  46   1 0.01
Thu 04/02 12Z 0.14 1313  94  49   1 0.01
Thu 04/02 13Z 0.13 1313  95  54   0 0.01
Thu 04/02 14Z 0.12 1313  96  41   0 0.01
Thu 04/02 15Z 0.09 1411  96  57   0 0.00
Thu 04/02 16Z 0.08 1410  96  63   0 0.00
Thu 04/02 17Z 0.10 1310  96  56   0 0.00
Thu 04/02 18Z 0.08 1409  95  52   1 0.00
Thu 04/02 19Z 0.08 1308  94  56   1 0.00
Thu 04/02 20Z 0.09 1310  93  70   1 0.00
Thu 04/02 21Z 0.09 1410  92  84   2 0.00
Thu 04/02 22Z 0.10 1412  90  90   2 0.00
Thu 04/02 23Z 0.10 1415  90  96   2 0.00
Fri 04/03 00Z 0.09 1518  93  98   2 0.00
Fri 04/03 01Z 0.06 1621  94  96   3 0.01
Fri 04/03 02Z 0.03 1623  94  92   4 0.01
Fri 04/03 03Z 0.04 1724  96  88   4 0.01
Fri 04/03 04Z 0.08 1826  97  70   5 0.01
Fri 04/03 05Z 0.12 1827  97  59   6 0.01
Fri 04/03 06Z 0.17 1928  97  50   7 0.01
Fri 04/03 07Z 0.21 1929  97  57   7 0.01
Fri 04/03 08Z 0.25 2031  97  55   8 0.02
Fri 04/03 09Z 0.31 2033  98  68   9 0.02
Fri 04/03 10Z 0.38 2135  98  62   9 0.02
Fri 04/03 11Z 0.44 2237  97  70  11 0.01
Fri 04/03 12Z 0.49 2239  96  76  11 0.01
Fri 04/03 13Z 0.56 2340  93  72  11 0.03
Fri 04/03 14Z 0.58 2439  93  60  12 0.01
Fri 04/03 15Z 0.63 2439  95  70  11 0.01
Fri 04/03 16Z 0.67 2438  95  74  10 0.01
Fri 04/03 17Z 0.72 2539  92  73  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.59 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